I think snails are great fun! Especially for the fish. One of my bettas was a tailbiter, and as soon as I put a snail in his tank, he stopped. The snail kept him entertained, I guess.
The one thing to remember about snails is that if they die, it's hard to tell if they're dead. I had a snail for months, and I guess old age started to catch up to him (no clue how old he was when I got him) and he started to slow down. He would stay inside his shell for days at a time. If he hadn't moved for a few days, I would move him and he would usually perk up and start moving for a while. He barely ate, either.
The last time I did this, when I went to poke at him with the net, I saw that he'd already started to decompose. It was pretty gross. And strange, cause the water didn't smell bad (I'd been sniffing whenever I would feed my betta, just in case). So I had to take everything out of the tank, sanitize it all, and put it all back together again. Blech!!!