Clear bra these days is much different than many years ago. It adds a huge amount of protection, and there are loads of videos on You Tube of folks showing the strength of clear bra by trying to puncture a sheet (not on the vehicle) with a key... It takes a lot of pressure just to even stretch the sheet, yet it never punctures through.
Back in the day (15+ years ago), clear bra used to turn yellow, not the PPF itself, but it was the glues used that would turn color. The technology and advancements in glue have come a long way and the yellowing no longer exists.
If you go with Expel or SunTek Ultra, most clear-bra's such as these have a proprietary coating (similar to a hydrophobic nano-ceramic coating) on the clear bra. These two in particular have what is known as 'self-healing' qualities. Light scratches will disappear when heat is applied or just pulling it into sunlight.
You can lightly polish clear-bra, but don't expect to do full paint correction and care must be taken not to generate heat on the clear-bra. One has diminished results trying to correct clear bra. You can add whatever LSP you'd like to, wax, sealant, SiO2/TiO2 etc..
If installed by a highly skilled installer, it should be done in such a way that you will NEVER see seams or lines, and no one should ever cut clear-bra while on the vehicle. A good installer will have all cuts required and tuck seams under body panels.
The idea of the clear bra is that it's the sacrificial barrier between the elements and your paint. When it becomes degraded, simply remove and reinstall. Much easier than repainting.
You can do a partial, or full frontal or wrap the entire vehicle. I have a full frontal on my 2016 Mustang Ecoboost. That includes; bumpers, full front fenders, full hood, lights and side mirrors. If you saw my vehicle you'd never know it had clear-bra.
Now onto the cons: Most complaints are going to be folks that suffered a bad installation due to the installer either not experienced or one who cuts corners (literally and figuratively) or both. A bad install will tun a customer off PPF and not want to ever do it again. My suggestion is to first research the clear you want, 3M, Expel, Suntek Ultra, and then go to their websites and see who are qualified installers. Research their reviews and ask the right questions...
I am redoing another Mustang because the original PPF job was terrible. The installer was inexperienced, left visible seams, stretch marks in the clear, and even cut the PPF while on the vehicle. We hope when we remove it, there will not be a line in the paint.
Again, do your homework... Having the PPF will give you the confidence to drive the vehicle more and enjoy it.
Hope this helps!