I don't have a REO. But, my ProVari 2.5s require 18650 Button Tops too, and Provape recommended the same AW IMR 18650. Maybe the REO isn't as finicky about battery length as the ProVari. Because I was having a hard time finding cells that would work I invested in a caliper. The AW IMR 18650 is 65 to 65.5mm. I bought some Samsung INR18650-30Q which are about 1mm longer and won't work in the ProVari. Fortunately, I've got other PVs that'll take 'em. But finding cells for the ProVari is a challenge. I won't buy again unless they give the dimensions in the ads. The caliper is great to have in my toolkit.
If you take your caliper to your battery, be sure the caliper's forks are insulated!!! I just used some adhesive tape, then zero the device.