It seems like a neat project but kinda silly. A small GBA screen is really a killer (if he somehow had video out then it'd be cool) and the controls are pretty worthless for a GBA, seeing as most everything worked fine with standard GBA controls. It seems like something suited for fighting games but I can't really think of the GBA being a great system for fighters.
The price is also outrageous. Nowadays there's emulators that can probably be configured to support similar gamepads, plus play on a big screen.