I got full tint (35% XPEL Prime XR) on the back glass (and sides, with 70% on windshield). I don't like the look of the half-rear jobs.
I was also concerned about loss of visibility, but luckily the shop that did my tinting (and PPF) had a Model 3 there with 35% on all of those windows, and the visibility is still great out the sides and back, and it's still a beautiful sky view looking up from the backseat. No regrets.