I did a long long time ago, but only on residential and commercial windows.

Automotive film does add a bit of security, but not very much. Mostly it will just keep the broken window together instead of blasting little shards all over your interior.


And as far as %, just go by the law. In Washington, on an SUV or truck you can go 35% on the front doors, and basically as dark as you want on the rear glass. But again, I'd check your local laws.