The great thing about the REO with an RM2 is you have RBAs covered with a squonk. There's not much point in me buying a Trident rda or short DID RTA (both 20 mm) for my tube mech. It's my 19 mm carto tank mod, and can be backed up with a sealed 510 to 510 adapter on a REO, which would also allow mounting of the Trident or DID. You really can do it all with a REO.