That would be really useful if you could test some GBA games with it to see if they work. I don't think it is really a problem if they need converting to run though as it's a quick process and only needs to be done the once before adding each game to the card.
What makes the DSOne so good? I've not read much about this cart. I mainly know about the M3 range. The price definitely looks really appealing. Does it run all DS games you have tried?