I've got a DSTwo, too. The gba emulator is a bit buggy (that plugin for DSTwo) but works for most games and is the fastest available since it uses the cpu inside DSTwo. Be sure to use cheats for the correct region and even then some won't work since most are made while playing gba nativly through a flashcard.
If a cheat doesn't work either look up another one or create one for yourself with help of a pc, an emulator like vba and its builtin memory editor. Most cheats have multiple approaches e.g. different pointer-to-pointer offsets, so a different approach could work with the dstwo emulator.
The reason why some cheats crash is because accuracy is traded for performance. If the emulator would be as accurate as a real console, you would only get 1fps even with a dstwo. So there is some hacking involved to speed things up and this can interfere with cheat codes.
Unfortunatly it is not possible to use the gba hardware (which is builtin in a NDS) through a ds flashcard. But you could buy a gba flashcard and use it to circumvent emulation.
