...the 3M product is the only one I'd recommend after seeing a couple different brands around the center I worked at. Like everything the F&I folks have for sale there's a List Price, a Internet Special, Washington's B-Day, etc. price and cost. And of course there's the let's make a deal price somewhere between Cost and List. My memory is a little faded on the exact details but I think a 328 went for about $1K list and we sold it for $600-$750 and our cost was about $500 with a warranty. The biggest problem was that some customers expected it to be truly invisible and well it is very visible but properly applied not too distracting. The key point is how it's sold: "Paint Protection" meaning if your put it on and drive for five years and go to sell your car, you can peel it off, get the border areas polished and the front facing surfaces will look new. I lease my cars and with BMWFS sweet spot at 36 months I don't want to be even a little distracted. If you are buying to keep and eventually sell and it hurts you every time you get a stone chip then do it. However, with the newer polymer paint systems that blend so well you can get a respray for about the same price and not look at the plastic film but also know that any respray on a car infers repair and trade-in numbers can tumble if any paint work is detected, even an innocent respray.
If you saw the cars that people singed on a statement had no accident damage what-so-ever and then saw the cars you'd become cynical very quickly. I had one guy sign for "no accidents" then after we showed him the wrinkles in the roof, the welds in the suspension tower, the missing bolts on the fenders because the holes couldn't align, and the paint rubbing off the side edges of the hood because the opening could never be squared up again finally admitted he'd been sideswiped and hit the center Armco barrier at 55 mph and was in the hospital for two days from being in that car that had "never, cross my heart", been in any accidents. And no, "Paint Protection" wouldn't have helped in that situation.