I went here for my tint/ppf. I haven't seen any pictures from the inside of the M3 rear window tint with a 2 piece installation so I thought I'd post some. Your mileage may vary on the quality of work since this shop seems to know what they are doing. There is also a video on their yelp page showing how they do the two piece tint.
These pictures are taken from the front seat, the back seat, and a close up of the rear window. From the outside you can't tell at all, so not really worth posting a picture of that.
This is also with 18% on the rear window, so a lighter tint will probably be even less noticeable. The way it is, you really don't notice it unless you are in the back seats staring at the tint line up close.