Great review! I pretty much agree with your conclusions. After several uses with the Wheel Brush, I had the same thing happen... the palm grip keeps popping off. I will epoxy it back on when I get a chance.
With the Tire Brush, I don't use any of the handles, as I like the palm grip better. Something tells that if I use the handle with it, I will have the same issue it in a short period of time.
I understand this issue has been fixed. There are several other issues with some of the GC Accessories that I'm keeping my eye one.