I have owned both the GNU (two years old) and the FLOW NXT AT (from last year). Even with the opening strap of the GNU, I preferred the FLOW. Much more solid construction.
The GNU's were good too, solid aluminum baseplate was nice, but the straps seemed flimsy. After a couple of hours the auto opening strap started sticking.
I've also tried the Cinch, which I didn't get along with. The tighter you have your straps, the harder they are to open and close, among other issues.
Much preferred the feel of the Flow's. With the new Flow strap technology I can't see a case for buying either the GNU's or the Cinch's.