I agree, permethrin is very toxic. Used in appropriate amounts it can be helpful treating mites but I wouldn't use it unless you need to get a handle on an outbreak. If you just happen to notice some minor mite symptoms, I'd work through the less extreme options first like DE and some of the mite spray that you can find in pet stores before I would use Permethrin.
Not saying it doesn't have it's place, just know that it's powerful stuff. A little goes a long way.
Dan