I have an FX Chrony and a Caldwell Precision Chrony. I tend to grab the Caldwell more than I do the FX, because I'm outside, usually without my phone.
The other day, when I compared one to the other, I found that the FX always reported speeds just a little slower than the Caldwell, anywhere from 10 to 5 fps slower, depending on the weight of the pellets. Heavier pellets found the two chronies to be closer in their readings.