factory window tint/film unfortunately do not provide any protection.
good quality tint wont change the darkness that much when seeing from inside toward outside, or, you can consider tint that has 70% or more.
I in fact have my windows tinted darker because X does not have the cargo cover in preventing intruders from peeking items in my trunk.
understand you want the flexibility, another suggestion is to buy and test out those sheds and let us know how will it go, if they do not work for you, return in 30 days.
(i just dont like the shade that can possibly fall off here and there, or not able to open/close windows whenever I want to)