Older Flex models had poor wires connecting the monitors, seemed to fray/disconnect at a high rate. Opening the button was easy but if I recall gaining access to the monitor was more of a pain. I have an older model with no issues so far, but I don't flip it all the way back. Maybe they fixed that with the current line up.
They're lower end lines, not bottom of the barrel, but decent specs with okay build quality. A step above the lowest end, but not as good as higher end models. Seems like they tend to go on sale enough to be competitive specs/price wise. For $600 it is probably an okay buy. I'd look into possible monitor issues before buying though.