That link looks like a great idea for large populations. Pond snails can move pretty fast when they want but I don't think they're smart enough to all go in at once. If you only have a few snails this method might be faulty (BUT it ensures your betta don't engorge on the bait)
Some people here just weight a piece of lettuce or blanched cucumber and hoist it back up when snails are on it. This method is quicker bc the snails don't have to figure how to get inside the tupperware and once you see even one snail on it you can haul it up.
If you're bent on killing them, they squish pretty quickly between the fingers. My bettas eat them! Or you can raise enough and sell them to a pet store or enthusiast who keep puffer fish. Sometimes assassin snails (which are supposed to be natural predators of pond and ramshorn snails) don't eat them and will prefer uneaten betta food and other meaty leftovers.
ETA- if you're careful about feeding your betta and are not feeding anything else in the tank, the ponds will self-regulate their population. If they have an ample supply of food they will reproduce. Mine never exploded in popuation because I did not overfeed, they snacked on algae until the bettas picked them off one by one over a period of time.