Among the number of titles that we reviewed on our recent sailing charter in the Seychelles, this and the Sarah Carpin guide book (both 2005 publications) served us the best. In fact, this book was so recently made available that it arrived 2 days before our trip and we elected to ditch the Lonely Planet for the Bradt.
The first 80 pages provides an informative guide - the background, history, and nature of the Seychelles as a visitor would want to know before arriving. The Carpin book covers most of the background better in terms of history and folklore (not to mention many, many beautiful pictures), but Mair/Beckley covers practicalities and resources (transportation, contacts, sport, shopping, etc.) much more thoroughly. (n.b. Carpin spent a number of years living there whereas Mair is a frequent visitor.)
As with most guidebooks to the Seychelles, the focus here is mainly on the 3 large inner islands - Mahé, Praslin, and La Digue - and again, the practicalities covered by this guide is unmatched by any of the others that we researched. Good maps, ferry schedules (current as of 2005), thorough reviews and contact information (including web) of many hotels and restaurants, and descriptions of shopping which, in an area that is somewhat resource challenged like the Seychelles, is an invaluable resource. (As we were sailing/self boarding, we were much more reliant on whatever resources/people we could pry information on where to find things as simple as dish soap or soy sauce. If you are going resort/package, as it seems most visitors do, this may be less an issue for you.)
Mair's road-by-road descriptions of downtown Victoria give you just about a shop-by-shop mental picture of driving/walking the smallest capital city in the world. Again, another reason why we pulled this book out time and time again on our trip. For car renters/day trippers, she gives an excellent point-to-point description for exploring Mahé and Praslin (the only two island that you can drive on anyways) on your own. Although Mahé is the largest island, and most often the largest and most central focus in many guide books, there is plenty of attention paid to Praslin and La Digue and more than sufficient practical information - including getting to and exploring the Valée de Mai and Anse Source d'Argent - to make this your primary guide to visiting those islands as well.
When it comes to the other inner islands (Silhouette, North, Curieuse, Aride, Cocos, Cousin, Cousine, Felicite, Bird, etc...) there's about 25 pages devoted to information about these wonderful spots, getting there, accommodations, and other necessities (if any - the islands that have facilities tend to be single-resort type). For most Seychelles visitors, unless some of these resorts are your destination, getting to these islands may be more of a day trip from your base accomodation so there is sufficient advice and information provided here. For folks sailing these isles, the information here is useful in determinine what is worth visiting (well, everything actually, but some are private and do not allow you to land) but of course you're going to need more information on harbors, anchorages and such. For that, we relied on the Pilote Cótier guide ([...]) kindly provided by our charter in the Seychelles.
Although we did not visit the outer islands, there are another 10 pages on most of the outer islands and 12 on Aldabra alone. Despite these places being generally less accessible, these notes should inspire you to a second, third, or so on visit should you have the means to return to the Seychelles. Again, good practicalities, although here I'd say the Carpin book does just as well and also has a number of spectacular photos of these areas. There are 8 full-color pages of photos in the Mair/Beckley book that should further inspire you to the beauty of this rare, delicate place.
Finally, a note about snorkeling and scuba-diving. Besides highly recommending it, if you intend to learn more before arriving, the Carpin book has a fairly good section in the back detailing the major dive sites which the Mair book does not. I believe that much of the information here originally comes from the excellent out of print Pisces Guide written by Lawson Wood. This isn't required of course - dive resorts tend to pre-plan the daily dive spots based on conditions, guest abilities, likelyhood of good marine life, etc. - but we found it helpful to know more about the locations that we were diving. Even if you are planning on doing a lot of snorkeling, I also recommend picking up the Indian Ocean Reef Guide by Debelius (expensive, but worth it) which will help you identify many many new sea creatures and corals that you will see on your trip to the Seychelles.