Have to agree.. I have many snails and they make such a mess of things and spike up the ammonia bad. There is one kind who is relatively clean, but in a 1 gallon it would be hard to keep him in there. If you decide to upgrade, make sure the tank lid is on tight.. had one climb out through the falling water of the filter and climbed out of the tank, over the top, down the front, then leaped off the counter and fell 4 feet and crawled under my chair.
They are a bit sneaky.. messy and sneaky. Their food is also messy - I have a lot of snails, so the wafers get eaten rather quickly, but when I only had 4, the wafer(s) would get smooshed all over the tank and quickly cause it to become cloudy - same with cucumbers if you aren't careful.
No need for a snail in a 1g, if you are just wanting another little pet, I would recommend no less than 3 gallons for 1 betta + 1 snail just because of the mess they create.