I would love to be able to do a proper review of the Stanley Gibbon's Ideal and Imperial albums. Unfortunately, I've never seen either in person, just cut out pages. But these pages together with images I've collected off the web provide, I think, enough information to make some comparisons between the SG Classic era worldwide albums and those of Scott, Steiner and to a lesser extent Minkus. Nevertheless, a lot of the following is incomplete and/or subjective and your milage will almost certainly vary.
As a reminder, the Ideal albums are currently sold in a three volume set which includes the World from 1840 to 1936 but no stamps from the British Empire. For the British Empire, you need the two volume Imperial Album. Unless otherwise stated all comments below are with the current version of the albums. (Earlier versions of the Ideal and Imperial each covered all the world, but not the albums sold today.)
PAPER
The Ideal Album's page size is 283 x 215mm and the Imperial's 280 x 215mm. These approximate 8.5x11 inches: i.e., smaller then Scott Blue and Brown albums but approximately that of Steiner. (I've seen two early ads for the Ideal that give the page size as 11.5 x 9 inches and 11 3/8 x 9 3/8 inches respectively.)
Older editions are on paper comparable in thickness to Scott albums of the same period. As for the albums being sold today, according to the 2012 SG accessories catalog, "All our leaves are acid free and manufactured without the addition of chemicals that would present a hazard in use. The paper is produced with a neutral pH value and meets ISO9706 permanence of paper." My guess is that the thickness of the pages is 130 gsm. I think 130 gsm corresponds to a paper weight of a little less than 90 pounds, but don't trust me on this. I believe the Scott Internationals sold today are printed on 80 pound archival quality stock.
Just as it is tempting to buy original editions of the Brown or pre-current editions of the Blue to save money, there are a number of tradeoffs to be considered for buying second hand Stanley Gibbons albums. As regards the Ideal, I don't know that it makes sense to buy an older version unless you can find one with interleaving. Otherwise you will be forever coping with stamps catching or rubbing against each other on facing pages. Even then, although the illustrative cuts are cleaner in the older editions, you album will be on thinner, non-archival paper. The one compelling reason to consider an old Ideal album is if you are able to find the matching British Empire albums which are no longer available.
While the Imperial album has stamps on the front of pages only, the issue about paper quality still applies.
BINDING
Like the original Brown albums and most of the Blues before 1955, both the Ideal and Imperial albums are hardbound, or as SG calls it, fastbound. However, unlike the Scott products, the current Ideal album is printed on only one side of the page eliminating the need for interleaving. As indicated above, The Imperial is effectively also single sided as spaces for stamps are on the recto sides of pages with catalog information on the verso. While that eliminates one problem with hardbound albums, two issues still remain: 1) what to do about stamps not provided for in the album since obviously you can't add pages; and 2) how to keep the album from bursting at the seams as you fill it up.
As to the first, the only real option is to maintain one or more additional volumes with blank pages (unless you go the stockbook route). As to the second, SG does provide a very interesting solution although I don't know how well it works in practice. That is, according to SG "Perforated, removable pages in the album allow for expansion without distortion, as your collection grows."
One advantage of the Ideal and Imperial albums from the standpoint of keeping an inventory or making notes about your collection is that the pages to be numbered. The Scott, Minkus and Steiner products are not paginated.
ALPHABETIZATION
Countries in the Ideal appear to be in alphabetical order, but countries can and do begin on the back or middle of pages. I don't know about the Imperials.
PAGE TEXT & CUTS
SG provides more info in its headers and often in the spaces than any other album. I particularly like their practice of putting the color underneath stamp illustrations. More than once I've been certain that I have a stamp in the right space in my Blue only to find out I've mistakenly mounted an identical design but different color that was issued in a different year. The Blue generally ignores watermarks, but SG doesn't so it is helpful that they include this information in the headers: i.e. "The permanent issues of Italy are all wmk. "Crown" and perf. Although better than the Blue or Brown albums, SG is inconsistent about indicating the purpose of a stamp or who is depicted. Many times the album says nothing at all, especially for definitives. Other times it is more helpful. Some examples of titles:
Austria: 1933 "Various Designs showing skiers"
Germany: 1875. "PFENNIGE" with final "E".
Hungary: 1933. Air stamps. Perf.
Italy: 1922. "Mazzini" issue
The Supreme Global also puts color under some cuts, and, next best to having the catalog on the facing page, includes catalog numbers. One attribute that separates Minkus from the others is that it groups stamps on a page over too large a date range: for example, the only dates on the second page of Italy are "Issues of 1870-1926," a total of 61 stamps. Minkus does go the extra mile by illustrating watermarks but my eyes find these too small to be as helpful as they could be.
Of course, if you want to talk about identifying text, you have to talk about the Imperial album where the stamp descriptions (really a little mini-catalog) are printed on the page opposite where you mount the stamps.
LAYOUT
Even though the page size of the Ideal album is smaller than Scott, the pages do not feel crowded to me. Nevertheless, one area where I feel the Blue is visually superior to either Minkus or SG is in the symmetry of its pages: i.e., Scott will choose to interrupt the denominated order of a set to arrange the horizontal and vertical issues aesthetically. Here is an example from the Ideal:
Within countries, the Ideal intermixes regular issues, commemoratives and semi-postals (just as do the SG catalogs). Airmails seem to be both intermixed and separated. I'm sure there is some logic to this but I don't have enough examples to see the pattern.
This intermixing is a help with some countries, such as Italy, which issued some sets that included both "normal" and semi-postals stamps. (I seem to remember there are even sets which have airmails and "land" issues.) On the other hand, when I'm trying to match catalog numbers, having the stamps in denomination order certainly makes things simpler.
While the Ideal typically supplies dedicated spaces for stamps, on rare occasions the album will be more free form. For example, there are two rows for Mexico 1916 revolutionary overprints without any spaces.
One very different feature of the Imperial Album is that it does not have frames around the stamps. Instead, there is a small box for each stamp to aid in aligning stamps on the page. If you are using mounts, this won't make a difference as the frame would be covered in any event. And, no doubt some collectors prefer their stamps sans frame. My preference, no doubt because it is familiar, would be for frames. I suppose I would have to see a neatly mounted collection in person before I would know for certain about the Imperial.
COVERAGE
The Ideal set contains spaces for around 37,750 stamps compared to 35,000 for the Blue Volume 1 and perhaps 80,000 for the Brown. While this may seem like the coverage of the Ideal is nothing special, remember that this total does not include any British Empire, ends with 1936, and essentially only includes regular stamps, commemoratives, airmails, and semi-postals, i.e., no postage dues, officials, etc. It also does not include varieties which I take to mean stamps with minor catalog numbers. Within these parameters, the Ideal aims to include stamps of all catalog values. In comparison to the Blue, then, the collector is likely to find a space for almost any stamp that falls within the SG album scope, where as the Blue is missing thousands of stamps that catalog under $1. And yet, because of the density of stamps on a page, a collection lacking the most expensive stamps will not appear as barren as with, say, the Steiner pages.
A big issue for collectors is whether they would feel to constrained by the Ideal including only regular issues, commems, semi-postals, and airmails. While I admit I wouldn't miss most Postage Dues and similar stamps that were left out of the Ideal, there are some issues I would be sorry not to see in a Classic era album. I assume, for example, that the Belgian Parcel Post/Railroad stamps from the early 20th century aren't in the Ideal.
I didn't do a lot of counting once it became apparent that SG successfully included the great majority of stamps that fall within its scope, but here are a few comparisons.
For Italy, SG has 60 spaces for 19th century Italy; the Blue 55 ('47 edition), the Brown 59, and Steiner 68. While we expect Steiner to have the most, it beats the others by including a Scott unlisted stamp as well as minor numbers.
For the entire period up to 1936, The SG
Simplified Worldwide Catalog lists 489 stamps for Italy, the 1943 Scott catalog, 508. The Ideal has spaces for 482 of these stamps (or all by 7 in the Simplified Gibbons), the Blue 391, the Supreme Global 445, and Steiner 521. (I am missing a volume of the Brown, but I would expect its coverage to be very close to the number of stamps with major numbers in the Scott catalog.)
From a layout standpoint, the Supreme Global gets all of Italy (through 1936) on to 15 pages, the Blue 18 pages, the Ideal 19 pages, and Steiner 37. The Supreme Global averages 30 stamps per page, the Ideal 25, the Blue 22, and Steiner, 14.
Since I couldn't do counts for the Brown, here is a look at 19th century issues of several countries for the Brown versus the Ideal. I've thrown in the Blue for grins. I've also included the counts for countries that are in the Minkus Supreme Global. I haven't gone back to see why Minkus has so many more stamps for Austria than the others.
Austria Brown = 70, Ideal=69, Blue = 43, Minkus = 131 (!)
Bavaria Brown = 71, Ideal = 69, Blue = 34, Minkus = 56
Germany (Empire) Brown = 49 , Ideal = 49, Blue = 39, Minkus = 50
Hungary Brown = 48, Ideal = 49, Blue = 23, Minkus = 50
Mexico Brown = 276, Ideal = 239, Blue = 77
Mozambique Company Brown = 46, Ideal=40, Blue = 11
Sweden Brown = 57, Ideal = 52, Blue = didn't count because of date overlap
The only country that the Ideal is obviously inferior to the Brown is Mexico. The Stanley Gibbons simplified catalog lists 281 stamps so I don't know why SG omitted 42 of these (presumably a lot of these are overprints--I didn't check). It does beg a question that I can't answer which is whether the coverage for the Americas is inferior to that of Europe. The Blue's best showing is with Germany, but is not in the ballpark for the rest (although, of course, I didn't look at catalog values which is why the Blue omits many stamps).
SUMMARY
What I think the Ideal best demonstrates is that it is possible to create a worldwide album that is comprehensive enough for many collectors but doesn't need to take up the entire shelf of a bookcase. And if SG still sold the complete Ideal, i.e., the entire world, and, especially, if they sold it looseleaf, I would be sorely tempted. Then it would only be left to decide what to do about stamps from 1937-1940.