I was very concerned about using an unregulated mod before I bought my Reo Grand (now my favorite mod by far). I could not understand how it could provide a decent vape as the battery drained from 4.2V to 3.4V as it was used. But after having one for several months now I use my unregulated Reo Grand + Reomizer 2.0 and Nzonic v3 + Hornet way more than my regulated mods.
I use a Reomizer 2.0 every day and I don't see a reason not to use an RBA on a Reo. From just reading they seemed too complicated, but after just a few tries I realized that the Reomizer 2.0 is pretty easy.
1) With an unregulated AW IMR 18650 1600mAh the bulk of the vape is at 3.9-3.6V so the swing is a lot less in practice. And you can always change
batteries sooner if you want to make it even smaller. I don't but to each his own.
2) With the Reomizer 2.0, or other RBA's built properly, the vape quality is very consistent through the voltage range described. I really don't notice the voltage drop at all. It just vapes all day long.
With those two points in mind I would not want to add complexity and failure points to get regulation. The way I vape and use my Reo Grand + Remoizer 2.0 I just don't see a benefit to offset the risks.