Strikes me there are 2 requirements.
Ease of registering a shot with high consistency over a long period with changing light and temperature conditions.
Near or acceptable accuracy of measurement.
I suggest a trial with all 3 chronos in a line, Skan, ProChrono and CED. If anything the fps should drop slightly by the third but not by much.
If they are as good as they appear to be the results should be spot on then it is down to price, choice.
I have no idea about absolute accuracy unless there is a high speed camera or some other timing device. I suspect the manufacturers have a standard rig that is/may be used and a correction applied for production.
The ProChrono was very consistent and worked very well out in the open, no idea how it would behave under trees, under a marquee, cold day, sweltering muggy, etc. So, I would not judge any chrono on just one day but over the series with samples in am and pm sessions.
With all three devices it ought to be enough to compare them and maybe even come up with a correction table.
BFTA Secretary 2012-2014
CSFTA Secretary 2014-2016