You'll never get the same result with a film as you do with factory tints, obviously. That said, i personally hate factory tinted glass as its always way too dark and i dont like the clear front windows and black rear windows unless its on a VAN!!! The RS has factory tinted rear glass and i wish i could change it and have uniformly tinted windows all round - but hey ho.
I always use Pentagon when i get any windows tinted on my cars - there is a local branch to me that now know me very well and take a lot of time to get the result as near perfect as possible as they know what a perfectionist i am. But again, its never going to be as perfect as factory tints and my biggest issue with film is around the micro dots at the outer edge of windows that very often withhold moisture and can look poo. But if you have to get it done then i personally recommend Pentagon.
E70 X5 xDrive35d M Sport - Carbon Black - Panoramic Roof - 21" BMW Alloys - BMW Performance Gloss Black Grilles - LCi Rear Light Upgrade - BMW 4.8i Exhaust Trims