Stomatella snails are my favourite! I love those little guys. I wish i still had some. I wasn't aware that Peppermint shrimp eat Stomatellas until I added a Peppermint!
The "Tufa" rock I've seen for sale in stores varies greatly. I wouldn't buy any of it though. I like the feedback, and looks of the "dry live rock" that you see for sale at places like
www.bulkreefsupply.com and it is affordable as well.
Personally though, I would cook all forms of dry rock as in the Guide in my signature on cycling and live rock.