I would argue that the ambitious player should puchase Marin and Watson if he wants to play the English!
Marin's rep book is limited to the 1.c4/2. g3 move order -- notably to avoid any possible transpositions into the Hedgehog formation (which Marin loves as black by the way). Watson doesn't cover every possibility in his volumes -- Musikmole describes quite well JW's intention with the 4 volume series -- but he does look at the 1.c4 and then 2. Nf3 and 2. Nc3 options, which can give rise to variations/systems not covered by Marin.
Incidentally, there is an old piece of advice which I first saw mentioned by Kotov in "Think Like a Grandmaster", although he probably isn't its originator. It is: study/learn a few systems in great depth whilst having a general knowledge of all the openings. Even if one never plays the Benko Gambit with White or Black, for example, it will enrich one's knowledge of chess to be aware of the typical ideas of the Benko. Did you know for example that Black, even though a pawn down, often can afford a queen exchange because it increases his positional pressure for the gambitted pawn? (It's a big surprise when you see that idea for the first time.)
With due respect, Marin's repertoire book series on the English (published by Aagard's Quality Chess) are miles ahead than the best book Watson ever achieved.
But that is a book series, not one book on the English. Sure, a person can purchase a multi-volume set on one opening, but I don't think that is what the OP is after, reading his first post. I guess it depends on your skill level and how much information you want.
For me, one book on the English is plenty, and I happen to like John Watson's writing style. I am not an International Master!