I have Crystalline 70 on the front windows, tint is barely visible and about equivalent to panoramic moonroof tint but still good heat rejection. Crystalline 40 all around the back (CA law doesn't allow front window tint but 70 is light enough to skate by). My parents have 70 on the windshield of their 328i. I thought about it but I don't like it on overcast days. I can't find a dealer that carries 90.
Crystalline tint is not pimp/limo by any stretch, but maintains a very classy look IMO.