The Cosco cup corners are a very well made product. They attach to the table and are sturdy. They do not move once they're on. The only reason I am giving them a rating of 4 instead of 5 is because the spot where your glass sits is more shallow than I think it should be. If they had made the holder an inch or two deeper it would hold your glass to the point where I don't think it could ever tip over. The way they designed it, I believe,you could tip your glass off if you aren't careful.