I'd first look at this thread before assigning blame: Paintball Radar: watch where you point it
Most radar-based chronos are capable of their stated accuracy specs and some are more accurate than their specs in general. This is because the tech is so 'old school' there are no patents to prevent anyone from doing it (which is why there are so many manufacturers).
This is something worth investigating- comparing the performance of the various radar chrono's to an optical chrono. I may actually be able to do this one.
One thing I recommend is that it's probably not a good idea to operate multiple radar chrono's simultaneously unless you have re-assurance that they are operating in different frequencies, or have other features to prevent interferrence.