The picture on the left looks like a bladder snail to me. I just got my first plants and that's the kind of snails I got. While they can overbreed, they are generally beneficial. Excess snails can be trapped, picked out by hand, squished or otherwise culled. They generally don't overbreed if you don't overfeed. I'm keeping my snails. They eat algae off the plants and decaying plant matter. I can't tell what is in the picture on the right.