Dear Andrew,
I use a Sekonic L-208, but NOT in the hot shoe (which, by the way, is not "hot" on the M2 and M3, I don't think-- you need a cable for the flash). I tried mounting the meter like that when I first got it, and it feels awkward. It is too big and oddly shaped for that use. You CAN put it there, but it is much easier to use it as a hand-held, compact meter. It is clearly labelled and it is well made. I always carry it with me when using the M3.
If you really have to have a meter on the "hot shoe", the consensus seems to be the Voigtlander is a good choice. There has been a discussion on it in the forum...
Best regards,
Juan