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.
I charged it overnight and it is reading fine again today. I've had the sunlight issue and will remember the cardboard shield. But these days I normally just I shoot a few pellets into an old car ramp (4 layers of 2x8) in the garage and the chrony is easily visible. I may still buy a more conventional chronograph so I can measure velocity while shooting groups. Hanging this little chrony off my two PCPs changes the POI. My shooting bench sits on an elevated side porch (so I can get more than the 25 yards distance from my back porch to the back fence where I hang the pellet trap) and I could easily put a little shelf on the handrail of the porch for a conventional chrony. But with this one working it isn't high on my list any more.