Well, I ordered one a while back and I'm just waiting on it arriving.
The main reasons I want one are
a) Convenient TV output
b) Drag and drop ROM support
c) Form factor
I love my GBA Player. In fact, it's my first console of choice but it's not portable. Being able to play all the games I like on the go and then being able to plug the unit into any telly anywhere is a great thing for me.
I have a couple of flash carts for my GBA but the proprietary software is flaky at best and it's dated and annoying. Drag and drop functionality has been a long time coming in my opinion.
I also loved the layout and size of the original GBA and this unit is as close as it gets but also has a decent screen and a rechargeable battery. About the only downside I foresee in the unit is that the AV output is only in mono but I can live with that.