The Watson book is miles above any coverage I have seen in these sites, although I must admit I am no subscriber of this particular site (Nimzo).

I am almost certainly sure of what I say because when I compare books to any sites here (the good / excellent ones, of course) books are always to be preferred. I find that the use of this site is for:

a) Lower rated players
b) Particular areas of discussion, that a book may not possibly cover
c) Recent ideas covered in updates. 

That the third applies to anyone below 2300 is very much doubtful

As an example Edward's Dearing book is 120% or Rowson's Grunfeld book certainly more useful than the general guidelines given here on the Grunfeld. Too much ground to cover. Of course Rowson doesnot touch upon the 10...Qc7 lines or 10...Bd7, (in the exchange, 7.Bc4 vars.) So best: buy the books AND subscribe to the sites, although one should know what to expect!

You might want to check the thread on the Flick-Knife Variation (which is basically another name for the same thing).

You will find some very good coverage on the Chess Publishing site if you subscribe to the Nimzo/Benoni section - the Flick Knife has been well covered in recent months.

Other than that, you might want to check out Endre Vegh's recent Starting Out: the Modern Benoni or Richard Palliser's new book (yet to be published).  Alternatively, there is good coverage of the ...Qh4+ lines in Watson's Gambit Guide to the Modern Benoni from a Black point of view.

Frankly, though, you don't need any of these - the coverage at the main Chess Publishing site is more than adequate