This will only work if you use two if these majesco links together. The Adapter will also. you cannot use one of these any other wireless link like the original. A constant blinking status light indicates a successful link.
While the product itself is a great basic idea, it JUST DOESN'T WORK!
I won't ask for a refund, but I will advise not to bother buying this. (You're better off buying a 3rd party wired multiplayer adapter for GBA devices, that is longer than the official 1st party wired multiplayer adapter for the GBA!)
Besides; if I wanted wireless multiplayer or co-op on the GBA? I'll just stick with the 1st party adapter; at least I know THAT works! (Despite the fact that it doesn't support that many video games for that platform!)