Wanted to bump this to make sure people see it. I used it this past weekend for .22 and it works even for that. The mic sensitivity is adjustable, you can delay timer start. Just has lots of functionality I like.
I used the Iphone apps for awhile. I got frustrated with it missing shots or picking up extra shot when shooting under cover.
I picked up the Competition Electronics Pocket Pro 2 Shot Timer and have been happy with its performance.