Considering how all these lights are long since reduced most places I've decided to acquire several of them and test...
The Gamester Trap Light, will having the external power source (excellent idea) has, as I said, blocked the port to the extent a GBA/GC cable won't fit in. Came free with my GBA, so I guess what do you expect.
Anyhow, my new attempt is with a Mad Catz "Light Grip". It uses the port, but has a passthrough on the top. The light is tremendously brighter and better than my old Trap Light, and provides much less glare. However, the geniuses who designed this thought the on-off switch for the light looked good on top of the thing, right next to the passthrough port. One can force a GBA/GC cable into it, but the notches that normally lock the cable in place switch the damned light to "off". Still, its excellent for single player (though I have not yet discerned what will happen to battery life)... and it only cost me $9...