I had my whole house done up with Q-Windows but did not do the door. This one was done from the onset during the renovations. Difficult to say whether it made any difference as I had other measures to keep the house cool. However in terms of noise there is a noticeable difference between the windows closed and open.

Also gifted my mum's house with Q-Windows for the front and rear as front has LRT track and rear is the LDP. LRT track is less than 50m away. This one was a retrofit. She did say the electric bill went down after the windows were replaced by around 20% especially during this hot season when the air conditioners are turned on a lot more. Noise levels? She can't hear the LRT any longer especially the maintenance ones that goes along the line at the wee hours of the morning. Traffic noise from the LDP? Barely audible after you turn on the air conditioning. In fact these days one of the problems is can't hear whenever someone is at the gate.

Personally, I think it is most useful for bedroom windows where you will notice the drop in noise levels especially in the late nights.