I have a CED8000. It's the blue one that folds sorta like a flip-phone.
It's OK.
It's small and handy, but I notice that I have never seen them in use by anyone who is good, or at any match, so that may say something.

I just wanted something to give me a random start signal, and I could check my time now and then.
I have found it pretty useful for things like:
-comparing how long it takes to change mags compared to pulling the backup,
-trying different methods of doing something (like weak handed draws),
-seeing if I really shoot faster with Gun A than Gun B, or does it just seem thatw ay,
etc.