Well I don't know if the features of the M3 one are available on any other card other than the M3.
When you turn the ds off, the point you are up to is saved in the GBA card (using the battery in the GBA card). When you turn the DS back on the save point is dumped to the Slot 1 card. It is good practice to do this straight after turning it off (you then dont have the problem of the battery running out loosing your save place)