I do wish that the diameter was just a SMIDGE wider. My Stanley does technically fit in the cup holder, but it’s pretty snug. If I have to pick it up to drink, it’s easier to just lift the whole cup with the holder still on it up off the table. To get the cup out of the holder, you have to either hold onto it while you lift the cup out or sort of twist your cup while you press it into to the side of the holder. So it’s definitely not the most functional when it comes to a Stanley cup, but it will still prevent it from getting knocked over, which was my main goal.
All in all, if you have a Stanley tumbler and need something like this just for daily use like myself, it’s a nice solution. If you need it to use in something like a moving vehicle or on a tilted surface, it won’t work with a Stanley. But if you’re just using it with a standard bottle of water or a beer can, it’s a great choice for wherever you need to use it!