I have had two of them...they kinda work ok but they sometimes fall off the glass when they hit an obstruction like a large real snail. (and keeps running, which will definitely get your attention from the noise of the drop and the fact that it stays running) As mentioned, they are loud when running so I set mine to run when i was not home.
I don't think they truly replace a glass scraper as its designed for light weight supplemental cleaning. Since its only running once a day you will still see light algae buildup that would only get picked up on the next run....and over time...you would find that those steaks (where it misses a spot) will require manual intervention.
The optimal use case would be if there is plenty of tank clearance and you want it to help polish your glass every day. Make sure you don't have many snails as I would end up having to flip them as they get knocked off the glass by its terminator version.