Secondary double glaze windows helps to deal with heat loss and energy bills. It is installed behind existing windows. There are also acoustic benefits in reducing noise levels trough sound insulation. But when it comes down to clean them, it could be very tricky as you have to take them out carefully and place them somewhere safely, where it won’t slide and you can clean them from both sides. We have just done a job in Bath recently, where we cleaned those types of double glazing windows. It almost took all day. We spent an extra time putting them back in as we had to fit them exactly how they were before.