i have premier put in the diamond cut tint on my e90 2011 last week. cost is about $200more than most other places. the quality and workmanship is exellent. 73% on windshield (not legal in cali) - very light, got it to give some uv protection. 50% on all other 5 panes (still on the light side, but hopefully, not attract attention from law...). 20% would look much more aggressive
i also have them install felt guard. they are around $16 extra per window.
they will do a one month check. at that time, they will fix any problems and touch up on the mat dot.
expansive, but top notch material and service with life time warranty.