I would expect it to be okay. There is the possibility that the betta might harass the snail by nipping at its antennae or stalks. A particularly aggressive betta might do that. Mystery (apple) snails are not that great at eating algae. Mystery snails may breed, as well.Nerites are another choice - they stay smaller, don't breed, eat algae, and are extremely well protected by their shells. There are different varieties of nerites you can get. For your tank size, a nerite is a better choice.
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