Sorry I have no experience with that product so can't comment on it's effectiveness. Provent-A-Mite is all I've ever used or recommend.

As far as where the mites came from, it could have been in some bedding, you could have been in a pet store or at a snake show and brought home a few hitchhikers, etc. Did you get any other new snakes lately? Anyone been over and handled your snake that might have just handled another snake? Take the snake out anywhere recently?

Mites have about a 30 day life cycle so whatever you do end up using to deal with them, watch for a hatch in about 30 days. If what you use only kills the adults but leaves the eggs intact, you'll be facing round #2 in about a month.

Last but most important, whatever you use read the directions carefully. Some mite stuff you put on the snake, some you don't. Get that confused and spray on the snake what should only be sprayed in the enclosure and you can seriously injure or even kill the snake.