Are the snails that come on the plants good or bad for my freshwater fish tank?
Snails aren’t dangerous to fish. They do, as you know, eat plants though, and can make an otherwise nice tank look kind of disgusting once it’s overrun (which happens very quickly- those common pond snails breed asexually so it only takes one to make one hundred). The ones that come in on plants are almost always considered bad because of that. I would remove those pond snails. If you still want a snail, you could try an apple snail. They breed sexually so you need two to get eggs. And their eggs are laid right at the waterline in huge clumps, so they’re easy to pick out if you do get some. Depending on the type of apple snail you get, it may or may not eat your plants. It’s pretty hard to tell the difference between the types and often pet stores won’t tell you exactly what they have. (and often even they won’t know) If you do get the type that eats plants, you can just feed it algae wafers or cucumbers and it won’t bother your plants too much. Good luck!
