I believe the problem with the Mite Off (I may have it confused with another brand, in which case I have no idea if it does anything at all) is that it only kills the mites. It will do nothing for the eggs that are also on your snake. So then in 30 more days your snake will be infested again.
Provent a Mite is highly recommended as THE mite treatment by many people I trust and it seems to always get the job done with a single application. However, if you don't mind spending the extra money to buy both products, the Mite Off will probably give your snake some relief while you wait for the Provent a Mite to arrive.