They can either be ornamental as well as a clean-up crew, or, you could use them for live food.
They are bred in a number of different tanks, with fish that don't predate on them, and I would recommend that you research whether the fish you keep will eat them before you purchase. Unless of course you are buying them as live food.
When the snails arrive, please acclimatise them slowly, and don't worry if they show little movement initially. This is quite normal, and they will soon be on the move once acclimatised.
I will post them to you first class, Monday to Friday only. The snails will be posted in a double sealed bag.
Posting will be first class, in a small box to protect the snails, and is small enough to fit through your letterbox, so no need to wait in for the post to arrive.