This product works on every surface such as Paint, Glass, Rims, Chrome, Rubber, Vinyl, Plastic, Fiberglass, etc.
But since it contains a bit of carnauba we don't really recommend using on genuine leather. If your car seats are made of typical 'car PU/synthetic leather' then yes you should be able to use it, although it may make them a bit slick. We are working on releasing our UV Guard very soon so that would be perfect for use on leather seats.
We also actually have an all new product that we are working on which will indeed work on every surface.
We are tweaking our Hybrid Wax formula to remove the carnauba and are very excited to release this new product in the coming months. It will be named Hyper Shine/Coat so be sure to be on the look-out for it!
The UV protection and water beading should last for several months. We can't give a definitive answer because this all depends on the climate and your washing regiment.
Furthermore, we are so confident in every product we sell that they are all backed with our Zero Risk Policy -- Use it once, or use the entire bottle!