Two Box Chrono
I don't recall seeing this posted before. I came across it while looking at the site for the auto trickler he sells.
$300 isn't bad considering that this system doesn't require you to shoot through it, the sun isn't a factor, and it doesn't mount to your barrel messing so you can use it during load development.
I have this one, similar idea but self contained.
I haven't done a whole lot with it but i'm not super pleased with it. Either my reloading techniques suck (entirely a possibility) and I have an ES/SD near 40 FPS or it's more sensitive to variations in alignment then they let on.
It also sucks batteries. The parasitic drain is horrendous.
Maybe this one will be better, but I'm gonna get a magnetospeed next time.