They are basically pet snails. They arent pests like ponds snails so that's a good thing. In fact, my frist aquatic pet were 2 mystery snails that I bought one and a half years ago. I added them to a 1.5 gallon and let them live in there for a year. Then I upgraded to a 10 gallon. Sadly, yesterday one of my snails died. When they die they release a ton of ammonia so be sure to get them out fast.
Anyways here is a website that tells you everything you need to know about Mystery Snails/Apple Snails (they are almost identical). After you read though it you can buy your self a mystery snail(s)!