Indoor shooting ranges are a no go. It was counting alot of other people's shots and reverberations. I did get a small break and managed to pull some 0.19 - 0.20 splits with A-zone hits out to 7 yards. It would work really well at an outdoor range.
If you really need a shot timer you can get a good one for under 130 bucks... CED 7000 ... That is considerably cheaper than exposing your iPhone to the elements of a shooting range. Just my thoughts.