There's a massive difference between a CRT at 30 Hz and an LCD at 30 Hz. A 30 Hz CRT is terrible in direct proportion to how bright it is, and it very visibly flickers. 60 Hz CRTs also visibly and annoyingly flicker with eye saccades, or if you wave your fingers in front of the screen. CRTs need to approach 75-85 Hz before they are all-day tolerable with white backgrounds.
LCDs have a continuous backlight and the liquid crystals need to change orientation to change frame. There's no flicker as long as they're showing the same frame. Here the flicker is noticeable as jerky motion, and is mostly just a problem for video, games, mouse cursor motion, smooth scrolling, etc.
I'm not sure if you're misremembering the Amiga flicker-fixer but the FF converted the 15KHz interlaced display of the Amiga to 30KHz (VGA style). It was the 15KHz interlace flickering that was noticeable, not the upgraded 30KHz signal from the FF.
I didn't write my comment clearly, with the FF it was not an issue, but without the FF the display in interlaced mode was painful. I had a long phosphor monitor which I used to mitigate that but until I got the FF it was an issue.
That said, the points above about the mechanics of LCD's being different enough that I might not object are reasonable. I've really not tried using a 30hz LCD display.
I'd be interested to see this display in action (not quite interested enough to experiment with $500 though) to see how it affected my vision of things.