You are going to find the same high compat. (arround 90-95%) in both slot 2 (NDS&GBA games) and slot 1 (NDS games only) flashcarts.
The highest NDS compat is in CycloDS, EZflash V, R4 Supercard DS (all slot 1) and EZflash IV lite, M3 perfect lite & G6 lite (all slot 2 flashcarts). Other products won't give you the same results.
If you want to check compatibility lists just ask.