Join Date: Aug 2006
Location: Lupin Information Super Highway/Goldfish Information Super Highway
There's one snail, Pomacea diffusa that does not eat plants. It's legal to ship that snail across other states and is also part of the family, apple snails (Ampullaridae). The other species though are illegal as they can indeed consume plants in vast amounts. Keep a spare tank just in case. Most bettas love to nip their eyes and antennaes out. These snails need to be supplemented with foods such as pellets, bloodworms, vegetables, algae wafers, etc. Make sure your water's pH is no less than 7.4 to ensure their shells will not erode from the acidic water conditions.
Your other choice is a lone nerite snail. They are finicky eaters preferring to eat algae only so unless you can provide constant supply of algae and biofilm, best avoid nerite snails altogether.