Incontinence clamp for jelqing?

I have seen on ebay incontinence clamps when searching for jelqing stuff.

The most popular brand seems to be Wiesner. I would link to their sight, but I keep getting errors. It is wiesnerhealth

Has anybody tried these, and how do they work compared to the tools with the two rollers? I have imagined that they might clamp too tightly for jelqing.