I know next to nothing about the BFRs... Other than that they're reportedly well worth the money.
I've shot the .500 S&W Mag out of a 6" barreled S&W revolver last summer. Only two light and two moderate loads.
You WILL know that it's gone off. And no matter the grip type or your grip on the revolver, chances are quite high that you'll feel it the next day. And day after that... and the day after that...
Might also want to cross-shop the S&W revolvers; see which one feels best in your hand balance-wise.