Its not "extremely low" and these people are flatout misleading you: look at all the people who ever had problems with the thing not booting up correctly ( ds saying there is no card ). Its unacceptably common, that failure rate seems to be pretty high on a particular batch of M3s that might be the one you got. As far as I can tell anybody who experiences the "card not recognized" problem can also experience the "no power at all" problem which can potentially brick the DS. Those are a lot more common than just "3 people" on this board and you know where it might lead.
Yes many of them do work, but you'll notice right away is a cheaply constructed product: the gba and rumble packs wont fit correctly and feel odd, the M3DS won't have the little plastic guides on the connectors making it likely to go in incorrectly and short out the DS ( which can eventually blow up either the fuse or the entire board like in my case ).
Use at your own risk, or at least know a place that could do cheap repairs ( a guy only charged me 40 bucks to replace the entire board but im pretty sure its probably more expensive than that but he had to do it like that since he was a few days behind in my repair )