I have 50 snakes, and I use it whenever I bring in new animals, regardless of where they come from. Not only pre-treating the Quarantined animal's tub, but preventatively treating the rest of the collection at the same time (you never know when you might still get a hitchhiker that you carry on you, despite your best efforts with a new arrival).
A can lasts me well over a year - it's a very small amount that you have to spray to treat a tub. However, I've been using it a lot lately, because these darn ANTS keep coming into my apartment (just in the bathroom) every time it gets below freezing. They don't make it very far though, I tend to get up each morning to a bunch of dead ants.
But, it's my personal belief, that every snake keeper needs to have a can of Provent A Mite always available to them as part of their husbandry supplies. I've never had a mite infestation, and I'll never be without a can of P.A.M.