Nice shooting machine DC! Maybe I will borrow some tips of your machine, and make my own...
I have a caldwell chrono too and I'm kinda satisfied with it. The phone app is nice, because you can get lot of data with it and fast. It has some bugs with disconnecting cable though..
At first the chrono only displayed errors, so I had to send it for repairs. Now I got a new one and it works nicely. Last time I got some errors, but like you said, it depends a lot on how straight you shoot through.