The RM4 has a fairly long 510 connector. Mine don't sit flush, even with the new 510 in the Reos.
But, aside from that, I may be in the minority, but I still believe the RM4 is one of the most under rated and over looked 'flavor' attys there is. It's a dinosaur, by today's standards; but still one of my favorites. Flavor wise, it's right up there with the Nuppin and the Manta.