I did use these for a period, but not now. I found that fish kept getting sucked in [I have some quite small fish in my tanks, and others spawn and fry appear]. Using a screen or mesh didn't work because the plant leaf bits that were also meant to be pulled in clogged it up. I finally took them off.
They are helpful for protein scums which can sometimes appear, but aside from this there is no advantage. And there are other ways of dealing with the protein, if it does occur, which in my case is now rare. And adjusting the filter return spraybar so it partially disturbs some of the surface will also help, though this can wreak havoc with floating plants. All my tanks have floating plants as I view these as essential.