Weigh up what it costs... a few quid and a job that could've been done better or a couple of hundred and a job that looks perfect and comes with a warranty.
All tints I have seen are on inside. The biggest challenge I have been lead to believe is the rear window. It bows not only top to bottom but also side to side.
Perhaps I'm too keen to give my money away but I would let the experts do it. At least if you're not happy then they have to do it again. The place I used also replaced both front window tints after nearly two years because it peeled on the corners ( coupe). How's that for service???
100% agree, get a pro to do it, if he F**ks up, he re-does it, and even when its perfect, will have a years warrnenty 9 times out of 10