I may have it totally wrong, but I think all adapters work about the same. The difference from one to another is usually the center post. If it's adjustable, try it just even with the threads. If that doesn't work, you can adjust it down just BARELY, so you have, at most, about a couple of mm's extending past the threads. What you don't want, is for the center post to extend too far down into the connection. That's what causes shorts and crimped or broken gaskets.
You have to, of course, make sure there's a hole in the center of the post, to allow you to squonk properly

I seem to recall some adapters that don't have a hole the
juice can flow thru, which, in other applications, may be just fine, but not on a REO.
It would also be a good idea to test the resistance of the atty after you attach the adapter, before you put it on the REO.
All that notwithstanding, I used 901 to 510, and 510 to 901 adapters for quite a few months when I first started
vaping, without a problem. I've always felt the 901 was a better
vape (covering my head and ducking), but I got tired of adapters, and not as wide a selection of choices, so eventually switched to 510 only. Nowdays, I can't even remember what a 901 vapes like
