I have 4 chronographs: Ohler 35P, CED, Magneto Speed, and a Chrony.
Have set them up in a row and fired a round with a known velocity and will have 200 foot extreme spread among them.
Had a friend come over with his CED and we set it up back to back with my CED. There was a 165 fps difference between the two alike CEDs.
I think the Ohler 35P is the best and most reliable but a pain in the but to use. I would give the Magneto Speed a high second and the Chrony the third place. Have no error shots with the Magneto speed, easy to use, and great product service.