They definitely can be a worthwhile investment, heres my feelings on them:
-The obvious benefit of no rock chips and being "invisible"
-Can be put in high wear areas to prevent scratches... such as door handle openings to eliminate those evil fingernail marks.... On the topside of back bumpers for those that use their trunk(and the bumper in doing so
)
-I have also seen it used on headlights which is a pretty cool idea especially if a lens is somewhat spendy.
However, what i have run into is that:
-The edges can be annoying to detail around (compound, wax, whatever you are using, often gets stuck up against the edge and can leave a nice line). It can be cleaned out but on the last car I worked on that had it some of the buildup was rather old and didn't seem to want to be removed. A good microfiber can often be used to remove most buildup though...
-Though invisible they tend to often times make the paint look overly orange peely.... Enough to where it can almost ruin a nice flat paintjob (which is the #1 reason i didn't put it on my car when i painted it, see below though)
-Make sure when installed all the edges and corners are wrapped on well, as I have seen on older installations that sometimes corners detach just on the edge and allow dirt to stick and turn yellowish.
-A few of the "precut kits" dont always fit all that well... I recall back to a Cadillac CTS that had the film applied where I work and while some pieces from the kit fit awesome, others needed modifying, which is why I would probably just assume cutting it yourself if you DIY it plus you can have extra to do any other odds and ends you think of that aren't included.
-Though i havent had a lot of time to experiment with the film, i have noticed it can be somewhat difficult to detail up with the rest of the paint as far as swirls and the extra gloss from my sealants etc. are concerned. I need to find a car that has this already applied that i can experiment with different products on...(and if you have any experience with it I want to know!)
Don't let this post lead you to think I am bashing the film, I am just laying out my experiences I have seen with it... And I do see myself putting it on a car in the future most likely... Though only in small portions. In a way i wish i had put it on some of the nose of my car as the car has a 2 color candy ghost fade paint from the lip up on the car and repainting it is... not an easy nor inexpensive (even though i do it for a living) task to accomplish...... and i have rock chips on it now