Ask them to show you engineering reports that document Chauvet LED to be compiant to the full range of refresh rates specified by the DMX512A protocol ratified by ESTA. I can look up the ANSI protocol number if you need it. But I'm betting they will not be able to. I was on the phone a week ago with one of their techs who said the flickering happens if you don't slow the refresh rate down. (DMX at its fastest is allowed to be 44.1Hz, and he said it works best around 25Hz. That's their fault, not the ETC and Colortran boards' faults. But you may be able to slow it down on the Express at least, I know that has a few options you can set.)
Another user told us that the board which Chauvet demonstrated these lights with which didn't seem to make them flicker was only sending out 192 slots worth of info, so it's like saying "this is a superhighway, and we accept trucks, but some of the bridges you'll travel under are 7' high, so you have to be under that, and we have a lot of construction all the time so you can't REALLY go 55mph or 65 or whatever it is in theory, because the construction crews that extend from one end to the other make you slow down."