I have one but today it appears to have essentially stopped working. I still get readings but they make no sense. In a string of about 10 shots I got from 178 to 425 mps. This is from my Avenger which I have previously measured at around 880 fps. Fill pressure was well above regulator setting for all these shots. I got a couple obviously incorrect readings before and recharging the unit fixed it. So I tried that today but it appears to have not worked. I charged it for a couple hours. I guess I'll try overnight and if it still gives me inconsistent and incorrect readings I will have to do something else (probably buy a "normal" chronograph).
Compared to the FX this unit is an amazing buy and if I only get a years use out of it I would still consider it worth buying. But my old conventional chrony worked well for over 10 years (when the light was right) and would probably still be working if I had not shot it.
Thing is you could of bought a higher end one and get that as well. This way you only out $30 not $100+ when it goes bad..
I've had to make sun shields out of cardboard for the sides the sun just right can throw it off or error. One day I had it on the barrel and when I cocked the rifle (springer) I seen the display flicker. So the movement through the sunlight was activating it. So I cut cardboard for the sides and taped them on , seemed to do the trick.
Lol.. I put this shield on to see the display in the sun