These have been around for a while and they work great. My DH created the exact same thing using a drawer pull and two window suction cups for displaying things. He made a hole in the suction cup and attached it to the handle with screws that came with the handle. Cost pennies. Oh, I think there was a little hook on the suction cup he had to remove.
Just sharing in case you want more than one for your classes. Hope your tendonitis eases up soon.
Jean

This handle is a lot bigger than any other I've seen, which is what I like about it. The suction cups are about 3" in diameter. For small rulers, you just use one. The smaller handles didn't seem to work very well for me, too hard to get a good grip on.

Annie

I agree it takes a big strong one on the long rulers. I used my for a while and then quit when my friend bought me this no slip film you put on the entire back of your rulers. No slipping. The one ruler wasn't clean enough when I applied the film so this year I took the film off and washed both the ruler and the film. Boy she's stuck now.
Jean

I prefer sandpaper dots to the film for a non-slip underside. I forgot to mention that the handle is most useful to me when I'm cutting with my right hand because I'm left-handed and that's the arm with the tendonitis, so I really can't hold the ruler quite as firmly as I'd wish, even with the non-slip surface. Because I'm cutting almost every day in addition to at least 4 hours a day doing FM quilting, anything I can do to protect that left arm is worth the investment!

Annie