From manufacturer of the grab handle. I’m sure if I emailed them about using it to carry glass they would respond that is not the intended purpose of the suction cup.
The ones sold at shopWCR sole purpose is for the use of handling glass. I have used for carrying 4x8ft double pane glass back in the day doing construction.
Also, imagine you’re the customer who is paying $1700 for window cleaning and you see a supposed professional using a temporary shower grab handle to handle your expensive glass.
That just my opinion, take it with a grain of salt. 
