FWIW, I've been using the RM4 a few days. Thanks to Quigsworth, I rounded the bottom of my screws before I started to use it. I'll run it a few more days, just to be fair, but so far, here's my thoughts (as a "mouth to lung" vaper):
Massive vapor if you take lung hits, mouth to lung, not so much, in fact, slightly less than the RM2.
Flavor is there, but I suppose, because of the size of the air chamber, not quite as intense as the RM2.
AFC isn't as useful to me as I expected it would be, even on it's smallest setting, too airy for me. But I run my RM2's with a stock airhole and find them "just right".
I managed to build dual coils (using silica wick) that came out around 1.4 ohms. I usually shoot for 1.8 ohms. Way more work than a single coil.
I miss the ceramic base, and I worry about a short with the screw heads in such close proximity.
I may be looking for a trade in the near future, but as I said, I'll give it a few more days of fiddling and adjusting.