I enquired about a Mystery Snail the other day and the lady there (who is great, she's quite knowledgeable) told me that if you have a betta that likes to sleep on the ground/gravel, give the mystery snails a miss due to their size.
One of her staff took one home and put it in the tank with her betta - during the night when her betta was sleeping on the ground, the snail was doing it thing....crawled up over the top of the fish and killed it.
I haven't heard of this happening before, but I suppose there's a first time for everything.
So if your betta sleeps on the ground, and your snail is quite large just be careful!!!
Alice - HMDT female 2017
Jupiter - VT male 2017
Fin - Rescue Fish 2017