We use the Caldwell chrono for Scots HFT shoots.
It needs a fresh battery but that's easily arranged by not leaving the battery connected after use. So far we've only used it with clear or overcast skies overhead (it uses ambient light to set off the sensors), and you need to shoot fairly straight over the 30mm or so slots, but it tell you if you've missed.
It comes with its own independently powered led light rack for fitting over the chrono in darker conditions, haven't tried that yet.
In my opinion it gives less variation than the Polish Air Chrony ( I also have), because the slots are roughly ten times further apart, so less sensitive to the angle of pellet travel.
It's the Indian not the Arrow