The Caldwell Ballistic chronograph I bought last year works really well and the free app it uses takes a lot of work out of collecting the data. I would recommend it to anyone.
It has been decent. At times I get readings that are nonsense. But that is rare. Only a 2-3 times in the 4-5 years I've owned it. The rest of the time it is very usable and I don't feel I wasted my money.