Provent a Mite and Nix both effectively kill mites.
Provent a Mite and Nix, if used improperly, both kill snakes.
The difference is that Provent a Mite comes with some common sense instructions that mitigate, but do not eliminate that risk.
There is no magic ingredient in Provent a Mite that causes it to miraculously have 30 days of residual activity. In fact there are several other permethrin sprays - like Sawyer's - that make the same claim.
If you like paying a little more money for a product that takes longer to get and comes with directions, by all means use Provent a Mite. However don't think that it's 100% safe and don't think it has some magic powers that other permethrin mixtures of the same concentration lack.