They're very good cleaners. None of the Petcos/Petsmarts in the area had them so I had to call a few pet stores/lfs to find some but I was able to. And then all of a sudden a month later my Petco had a ton of them.
My bettas don't mind them at all. I got a Mystery snail once and Fishie tried to kill it. But nerites don't come out of their shells very far so to a betta they just kind of look like gliding rocks.
Or if you have a larger tank you can have 3 or 4 Otos.