This item's not that bad. It turns your GBA into a tv or a TFT monitor. It includes video-in so you can plug you carputer into it. Watching local TV is the bonus. This is a great product for people who just got the GBA SP and don't know what to do with their old GBA. Or are extremly tight on money.
You can really impress people if you can figure out how to broadcast your carputer desktop into UHF or HF signals so it makes your GBA look like a portable computer or one of those new PenTabs. This is a very cool way to all of the passengers experience carputing. And you dont have to worry about them breaking your expensive LCD
EDIT: personally i'd get it cuz i sometimes have a bunch of kids in my car. And i can slip two or three into the 'magazine' holders on the backs off my seats and they'd all share the same UHF signal so no additional wires. Or at competions, i can just hand someone standing outside my car a GBATV and demonstrate without anyone having to get in. (dream on)