Bought one of these CED M2
chronographs three weeks ago and have had no problems with mine. Just make sure you use a new battery every time you set it up.
When I first set it up I did experience some extremely high readings because the unit too close to my big booming 30-378 & 338-378 Weatherby Accumarks.
It actually recorded speeds of 3900+ fps for both which we all know is impossible.
I moved the unit further away to the maximum length of the cables and was back to sensible velocities.
My previous chronograph was a Chrony which although it "served me well" it did however tell quite a few lies.
The accuracy of both of my rifles is excellent but the recorded E.S. on the Chrony was far too high for those E.S. readings to be true.
The Chrony also recorded speeds which were at least 100 to 125 fps higher than those recorded in reloading manuals.
Also throughout the morning the Chrony recorded erratic speeds for my 338-378 pushing the 300SMK pill from an average of 2830 fps to 2850 fps and then up to 2890fps with E.S. varying from 72fps to 125 fps.
The CED M2 recorded speeds that were more realistic and reflected what the reloading manuals stated.
I neck anneal all my cases after each shot, weigh and batch my cases, trim them to length and load carefully weighed charges of powder which are first thrown and weighed through my RCBS Chargemaster and then a second check is performed on my beam scales.
The CED M2 chronograph
now records my E.S. for my 30-378 at 7 fps and for the 338-378 it is 12 fps.
The 30-378 delivers 3 shot groups of under 1/4" and the 338-378 is good for 1/4" to 3/8".
For accuracy and consistency I can certainly recommend the CED M2 chronograph.