I tinted the front two windows to 35% to match the privacy glass and here's my $0.02. The windows match well but not perfectly - average person couldn't tell the difference but a car guru definitely could. Also there have been many times in daylight that I wish I had gone darker, but more times at night that I'm glad I didn't! I had 20% on my other vehicles but I guess with age my night vision has deteriorated.

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2002 BMW X5 4.4i