I am somewhat new to the clear bra world. Having just bought a new car and hating rock chips I ,like you, have been doing lots of research. I now own three full kits for my car. All the kits bought off e-bay from the same supplier. The first kit they sent me was 3mil. I wanted 8mil so I ordered, their 8mil. Now they sell a 3M 8mil kit. So I bought that as well.
I did all this buying while I waited for warmer weather to attempt the install. Found lots of install info on line including video installation instructions online and Youtube. The installations tools are cheap and readily available. I also have 20' of uncut material that I am custom cutting for various exposed places including the trunk lip and front 12" of the roof and pillars.
I have installed some of the pieces that don't require alot of stretching such as the trunk lip, roof piece, mirrors,side fender bits and main grill and hood portion.
I am using the so called cheaper film for the most part to develop my skills.
The results have been great, near perfection. When I go to tackle the full front bumper, I intend to use the cheaper film. It will be tedious. But I am hopefull it will look good.
My advice, practice with the cheaper film before installing 3M and follow instructions.
Don't be in a rush, prep surface,clean hands and work area.Warm ,wind free environment.
No hairy dogs or cats.
On my silver Camry Hybrid I can't see the difference in the film quality. Only time will tell.