I am one of those whose car has dark tinted windows. Although not like those cars from M'sia, some of which are practically pitch black.
When I brought in my car for window tinting, the main consideration was heat rejection and aesthetic. It's ridiculous to have the front like 75% and back 90% tinted because the end result is awful. It disrupt the natural flow which car designers had so painstakingly designed.
So I settled for a compromise and tinting my windows front 85% and back 85%, which is illegal by LTA standard (at least the front is). It was money well spent as the car remains relatively cool even parked under the hot sun for some time. (p.s. the % numbers are guesstimate, as I don't bother to remember such ratings. I only know my tinting is illegal that's all).
So far I had no issues with law enforcer, but when my car reaches 3 years old and have to be brought in for inspection, that's probably where the problem starts.