My wife just got me the Moga Ace for Christmas and I LOVE IT! It definitely isn't worth $100, but my wife got it from Best Buy (so she saved $20). The first thing I did was load up GTA: SA and it kicks the crap out of using the horrible touchscreen controls.
I will say that the reviews are right about it being kinda cheap. The shiny plastic on the top of the controller around the buttons/analog controls was already scratched up before I took it out of the box.