Review on Heavy Duty Aluminum Glass Suction Cups - Vacuum Plate Handle Glass Holder Hooks for Easy Lifting of Large Glass/Tile - Suction Cup Lifter/Moving Glass/Pad for Effortless Dent Pulling (2 Pack) by David Pullen

When they work, they're great. I use them to open and close very heavy soundproof windows that don't have a handle and are difficult to manoeuvre. They had been working for a little over a year when one of them suddenly fell off. There were rubber marks on the window that were difficult to wipe off. After getting rid of them and rinsing the cups and window thoroughly with rubbing alcohol, I reattached the suction cup. However, he does not stay at the window for more than 12 hours. I'm pretty sure it's because the rubber is separating from the cup. There is no sunlight coming through the window so I'm not sure why the rubber came loose. The one that's still running gets about 2 hours of sun a day. 5 stars for this one and 2 for the one that no longer works. However, because of the price, I can repurchase and hope for the best. I understand that they cannot be used permanently, but once they come off and are reapplied, I expect them to stay for a much longer period of time. Time is not 12 hours.