I bought a bottle about six months ago when my new corn snake had mites. I found it extremely effective against mites. In fact, one treatment and I didn't see another mite until months later on another new snake.
However - just anecdotal and NO idea if its related to Reptile Relief. The corn snake I put this on was a hatchling creamsicle who was perfectly normal in appearance and behavior at the time. The directions said it could be sprayed directly on the snake but as this was a hatchling, I was reluctant to do that, so instead I sprayed it on her paper towel and put her back in the enclosure. For the next two days, I thought I was going to lose her. She was very lethargic and barely moved. Finally she started to seem more energetic, shed and all seemed well. Several weeks later, I noticed that she was holding her head at a funny angle, a trait that worsened as the weeks went by. Then I noticed that she didn't seem to have much upper body control and would kind of flop around, whether she was in my hands or in her enclosure. She continued to eat vigorously. I took her to the vet who just suggested we "keep an eye on her" whatever that means!
She just shed again yesterday and is still eating enthusiastically and growing well. However, she is what I describe as "spastic". Her head is always at a 90 degree angle to the substrate (in fact, I almost took a photo of her this morning and if I had posted it here it would have looked like a photo of a dead snake as she was lying kind of coiled but with her head completely on the side), and she continues to have difficulty controlling her upper body.
Now - whether this is a genetic condition that this snake would have developed no matter what, or whether this is a result of the Reptile Relief treatment, I will probably never know. However, the next time I had to worry about mites, I used the dish soap method of treatment rather than the Reptile Relief, just to be on the safe side.
Make of this what you will