The material on the Modern Steinitz proper is very good, but IM Taylor cannot resist the temptation to make this a "repertoire" book by including material on the Exchange variation. The 35+ pages tacked on to the end therefore comprise 10+ percent of the book, have nothing to do with the Modern Steinitz, and are just plain bad.
IM Taylor apparently is sick of the drawish Exchange variation with 4...dxc6 5. 0-0 so he instead recommends 4...bxc6?! which just plain sucks. He complains that other authors have been similarly disparaging toward the line without really analyzing it, but then he makes the same mistake about the Exchange line with 4...dxc6 5. Nc3 -- after 5...f6 he opines that 6. d4 is "necessary (due to) 6. 0-0 Bg4 and White can't get d2-d4 in." I'm sorry but I'll hang my hat on the experience of a former World Champion over one sentence of IM Taylor's -- there are other 6th moves for White and considering that Taylor begins the book with over 15 complete games by former World champions, he should know better.
This myopia carries over to other variations too. For instance since IM Watson thinks 4...bxc6 is viable against the Exchange variation, he thinks little of the line 5. Bxc6 bxc6 for White in the Modern Steinitz proper. And between his myopia and his veneration for the games of Keres (a grandmaster who was about as strong as World champions in his day, and who Taylor has made the "hero" for this book), he disregards improvements for White. For instance he follows the game Mecking-Keres in this particular delayed exchange variation on pp. 53-55, and he makes a big deal out of 9...Rb8 and how another author didn't even consider this move or game. But then he glosses right over 10. b3 as played by Mecking without considering alternatives for White, which I found in my own database (namely 10. 0-0).
Either Taylor's database is smaller than mine, or he chose to ignore this; neither is a good indication, particularly the smaller database, since I am nowhere near IM strength (rather, class A/B). Rather I think IM Taylor's tunnel vision may be at work again when it comes to evaluating the quality of games in the database. For instance, in the line of the Siesta variation 5. c3 f5 6. exf5 Bxf5 7. d4 e4 8. Ng5 d5 9. f3 e3 10. f4 Nf6 11. 0-0 Bd6, he writes "the soundness of the entire Siesta may rest on the evaluation of the obvious 12. Bxe3, which has never occurred in a high level game". My database however shows that International Master and many time Latvian champion Vitolins drew as black after this very move (there's a wikipedia article about him). Again, either IM Taylor's database is not sufficiently up-to-date, or he did not recognize the name Vitolins, in which case he needs to broaden his team of research assistants (especially when he makes such a bold statement about the viability of the Siesta), because to me Vitolins was readily recognizable when I saw it in my database -- he played lots of correspondence games in the Latvian Gambit (and Watson claims to have used databases of correspondence games).
The material on non-Exchange variations of the Modern Steinitz proper with 3...a6 4. Ba4 d6 does seem well worth it. Bear in mind though due to the lightly annotated complete games format, you are still going to have lots of work to do on your own if you plan to add the Modern Steinitz to your openings arsenal, because the annotations are inconsistent: usually sparse but insightful, occasionally deep, but often insufficient. I'm already coming to different conclusions for instance in the Yandemirov gambit, so you need to do your homework and not follow everything blindly, just because an IM says so.