That one was in activity about the same period I took the Montparnasse station somewhat regularly, and over those years I couldn't ever take it as it was always either broken or running opposite to my direction.

I do think a concept with parallel tracks moving at different speeds would have been easier to use and more reliable though. But it might not have been revolutionary/over-engineered enough to attract attention and subsidies.

Man, they should've designed it similarly to the video, with parallel tracks with differing speeds. But people's lack of attention would probably lead them to park a foot on each track and causing a tumble.

Speaking of speed, in the Stockholm main station the escalators go faster than others I've experienced... But I don't know if they've adjusted the speed since my experience years ago.

Decomissioned but still rolling, just slower.