You are correct.
Seen Venture Shield etc (all 3M products I am told) on cars and the paint surface looks very strange.
Edges can turn slightly yellow after sometime. This is especially visible on white cars.
I would have to dissagree on the finish...I had it on a car from new (5 years) and when polished up with decent products, you couldn't tell if it was paint or Defendall film.
And after 5 years of hard driving...no stonechips...only a couple of small nicks in the film on the lower spoiler.
You could see an edge though, where the film stopped part way up the panels, as you'd get a line of polish/wax highlighting it.
Can't comment on the yellowing...as it was on a yellow car!