I'm getting an M3 and passcard 2.
Well, eum.. Your being contradictionary

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What I meant to say was would I need to get a passkey device or am I fine with just an m3 mini sd and passcard?
You say your going to buy a passme2 (the passcard 2), and then you ask if you need a passme (1/2).
So if your buying a M3 and a passcard 2 you will no longer need to buy a second passme (1/2).
If you only buy the M3, then you need to borrow a passme (1/2) once to install flashme.
One thing is better (not counting power use and something sticking out on your DS) and that is less risk of bricking.
Because of the safety code in the flashme firmware, if you brick your DS you can restore it.