Andrew Soltis has written some of my favourite chess books. He has also written some chess openings books that he obviously has not put sufficient effort into.
His relatively recent "Transpo Tricks in Chess" (Batsford 2007) seems to fall in between these two main groups of Soltis books. It's a kind of 'Chess Openings Transpositions Encyclopaedia' but yet a surprisingly easy read. As one had to expect, its coverage of different openings is a bit uneven but generally it's quite good. Soltis doesn't cite his sources extensively and is often a bit brief. Consequently you sometimes have to wonder how trustworthy his evaluations and suggestions are. There is however little doubt that he knows a great deal about the book's subject. Soltis was a strong player and is good at conveying his knowledge to the reader.
I had a check of the London System and the Dutch Stonewall and was not particularly impressed but then there was nothing obviously wrong either. His coverage of the Closed Ruy Lopez was much more interesting. His explanations of the old 8...Na5 variation (the Proto-Chigorin) are very thought provoking. I must make a closer study of that variation when I can find the time and then Soltis will be among my main sources (together with Larsen's and Radulsky's games).
However, what really made me raise my eyebrows was his (surprisingly brief) comments on the Zaitsev variation. He writes that 'Zaitsev's original move order [9...Re8 S.J.] is inexact if Black wants to avoid a draw [9...Re8 10.Ng5 Rf8 11.Nf3 S.J.] as well as the complications of 9...Re8 10.a4 Na5 11.Ba2. More precise is 9...Bb7! first and then 10 d4 Re8, transposing.'
(Position after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.0–0 Be7 6.Re1 b5 7.Bb3 d6 8.c3 0–0 9.h3, when Black can head for the Zaitsev with 9...Re8 or 9...Bb7)
In this brief passage there are two quite remarkable claims without much supporting analysis or explanations:
1) Soltis indicates that it's easier for Black to avoid the draw after 9...Bb7 10.d4 Re8 11.Ng5 Rf8 12.Nf3 than after 9...Re8 10.Ng5 Rf8 11.Nf3.
2) Black may want to avoid the complications after 9...Re8 10.a4 Na5 11.Ba2.
The first statement is more than adequately covered in 'The Ruy Lopez: A Guide for Black' as Flear indicates something similar in his 'Ruy Lopez Main Line'. We conclude that exactly the opposite is true: the move-order 9...Re8 gives Black some extra opportunities to avoid a draw by repetition. I so far have no reason to doubt this conclusion.
Statement number two is more worrying: In our Ruy Lopez book we do not discuss 10.a4!? as a possible reply to 9...Re8 at all. Did we miss something very basic or critical in our research?
A quick check with my database was enough to calm me: There is only one high-level game with 9...Re8 10.a4 - Kholmov-Hennings, Chigorin Memorial 1973 (which is actually a couple of years before Igor Zaitzev developed his system!). The game continued 10...Bb7 and although White won the game, Black appeared to have a fully playable position after 20 moves. The game did nothing to reduce the interest in 9...Re8 and 10.a4 has had no other GM outings. I could find no examples continuing 10...Na5 in my database.
A check with Rybka and Fritz confirmed that we hadn't missed anything very basic. 10.a4 starts up around 6th place on their list of candidate moves but slowly climbs upwards. After a couple of minutes it seems to stabilize somewhere around 2nd to 4th place with an evaluation very close to '0.00'.
This of course doesn't exclude the possibility that 9...Re8 10.a4 Na5 11.Ba2 is an important variation for the understanding of the Zaitsev variation. If there ever is an update of our Zaitsev book, it will certainly be mentioned. However, I suspect it will concentrate on the natural 10...Bb7 rather than on 10...Na5.
Returning to Soltis' book: I believe my experience could well be typical: As a grand overview over move-order tricks in the opening it's about as good as you could possibly wish. However, if you have researched a subject yourself, you will probably find Soltis book a bit superficial or even disappointing. However, there is also a realistic chance that you could also stumble over something really thought-provoking.