In my testing of the MU Plug with BH209, ALL the primers have worked without so much as a hiccup. I have tested the Rem 209-4 (410 primer), Rem Kleanbore, Rem STS, Win 777, Win WML209, Win W209, CCI, CCI 209M, Federal 209A, and probably a couple I forgot. Never had a problem with any, as the flame only has to travel approximately .200" through a generous flash hole.
If you want the hottest, get the Federal 209A or CCI 209M primers. If you will be hunting in damp conditions, make sure to use the o-ring, it seals out weather as well.