IIRC Gayle stated that he chose a hollow grind to bring out the best in M4. Because the steel is tough, it can handle a very thin hollow grind while still having enough blade strength for hard use.
Yes, I do like his hollow-grind blade. The shoulder-to-shoulder width of the edge is a little narrower than my Military M4, which I like. (But not as good as my Sebenza.) And I've done no testing, but I'm sure the GB is a great cutter. However, I really, really like the Military M4. My comment was comparing these two blade grinds. The spine, like the edge, on the Military is a little thicker than the GB, but the distal taper is much more pronounced, so in a wide variety of conditions, I suspect the Military -- which is longer, pointier and thinner near the tip -- would be a somewhat all-around better cutter between these two excellent cutters.
I also like the heat treat that Spyderco puts on its M4.
My big complaint is the lack of relief in the liner and scale to aid in the one-handed release the lock. I see no upside to this design feature, and it's a PITA to release this blade with one hand, especially if your hands are cold or slippery. It's not too bad to release using both hands, but I like knives that can be opened and closed easily with just one hand.
The other two issues are just aesthetic. With liners this thick, the carbon fiber scales are there just for looks and grip, not strength. And this checkerboard stuff doesn't look all that good, especially when undersized to expose the liners.
I'm going to see if I can find someone to put on some nicer looking scales and grind a thumb relief into the scales and liners. Maybe then I can give this knife a little love.