I have a PACT that I'm learning to use, but I'm having some success with it. Not 100%, but not too bad. I like that the instructions that came with it say "don't suffer in silence! If you're having problems, call us and we can sort you out". My PACT was having some issues with not seeing a lot of shots, erroneous readings, etc. I called, they gave me a dew more tips, and it's working better now. All in all I like it, even if it was a little pricier than the least expensive chony's like the one below.
I borrowed a Shooter's Gamma Chronograph for a few months and did not care for it. The features and etc it had were nice enough, but I never did get accurate readings off it except for 22LR. Bad readings, no readings, I had no luck at all with the dumb thing. Even had a few people with chrony experience come over and help me with it, and they couldn't get it to work right for anything but 22 either.