The last thing I want when struggling with a heavy window during installation is to drop it. Even small falls can fracture the flange, making for a time-consuming repair. After watching my glass guy use suction-cup handles to install large glass panels for a shower enclosure, I had to get a set. You can get a good cup for less than $100. I have two, one for my window-installation partner who stands inside the building and passes the units out to me, and one for me to grab hold of. The cups pay for themselves both in time saved handling windows and in the peace of mind knowing I have a secure hold of an expensive piece of the house. Just one caution: Remove any plastic protection sheet on the glass before applying a cup.
Mike Guertin, East Greenwich, RI