Exactly my practices as well, it does keep everything clean if/when something
happens. I also have an assistant that is very well equipped, and rent from him
often. I'd rather see money go his way than the local rental house.
As long as they use it in my studio, no problems.
But whether they want to use in or outside of my studio they a) have to replacement insurance and they should also have ther own liability insurance if they are bringing clients or others (stylists, assitants) into your studio.
If it is a paying project I think it is fair to charge rental fees and here's why: equipment does need to get replaced as it gets used and the rental fees go into that replacement fund. You might not charge them the same amount a rental house would charge them but they should pay something.
It also helps to keep the personal and professional sides of the relationships clean. Also don't forget that this is equipment you use to pay your rent/mortage as well.