Hmm.. assassin snails are strictly carnivores. They'll stick to the substrate for the most part, as they burrow into it to rest/hunt. So if yours is going around the glass cleaning a lot, its likely not an assassin.
What does the shell look like? Can you share a pic? An assassin will have the infamous siphon on it too, check to make sure yours has one (I attached a screenshot down below of multiple bumblebee assassin for you to compare with).
Also, since they use their siphon to get up in other snails' shells to eat them, if the other snail is too small and their siphon won't fit into their shell, they'll typically leave it alone until it's bigger. Normally they'll go for the common types of 'pest' snails (when big enough to fit siphon into, I've read they'll eat eggs too) or snails their own size and larger. I've heard of multiple assassin snails teaming up against larger snail varieties.
Another big thing to remember about them, is they might eat up to 4 snails every couple days (1-2/day or so). If your other snail population is booming enough, 1 won't get it under control you may have to remove some manually (if that's why you got it). If the population is too small, your assassin might go through it quickly and you'll need to provide feeder snails or something.
I would keep 1 to avoid breeding.
As far as the rest of the thread goes, seemed like a lot of unrelated reading.. so don't think there's anything really I wanna add. I'm betting all the bases have covered by now anyway.
