I have the CED 8000.
It has a lot of features with different types of timing, but the most basic part is that after you (or another person) presses start, it waits a random amount of time, then beeps and times your shots after that. It gives you a total time and the time between each shot.
I like it a lot, but it was not cheap ($150, I think?). I got it from Brownells. No one near me had one in stock.