in a way they're good they help eat algae and leftover foods but also bad b/c with time they will be all over ur tank
several ways to get rid of them is by the simple yet constant *crazysmiley* of these lil buggers u can get a clown loach if it can be in the tank with the other fish u got and they will eat them all up, i think other fishes could eat them too my betta loves eating them, u can also try putting a piece o lettuce,food, whatever snail likes in a lil bottle or something and let it sit overnight and see if any snails get in the bottle, i have a ten gal with a bunch of them and it's no big deal sinnce i feed them to my betta and once to my clown loaches but they have all died recently :'( but anyways it's a nusiance when they are all over ur tank, don't use those snail killin chemicals it might hurt other things in the tank i'm starting to hate those bigger snails i just got one a bit bigger than a golf ball lfs called it bluesnail and it ate all my vals to the roots overnight in the 10gal tank >
i put it in the goldfish tank now since there's no plants in there