Well it works great as a GBA cart, no funny stuff involved, but I haven't tried running DS game(s) from it.
There is a patcher program (or two) to patch roms, but I'm sure it's gonna be hit and miss on what DS stuff will run from it. You'll still need a passcard in the DS slot or a flashme'd DS for that to work.
..and the DS won't play the older Gameboy/GBC type games, but you knew that...