I have two:
Competition Electronics Pocket Pro II
Competitive Edge Dynamics CED7000
The CED7000 is smaller, small enough to fit in a shirt pocket. The battery has to be recharged.
The Pocket Pro II is larger and uses a 9V battery.
The CED7000 has a higher pitched beep than the Pocket Pro II. I have had some shooters say they can't hear the beep of the CED7000.
One big advantage of the Pocket Pro II is the 9V battery. If it goes dead at a match you just stick in a fresh 9V. If the CED7000 goes dead you are out of luck as it takes an hour to charge.