Ok so I played with Sheldon's calculator and find my gut feeling was not right - gain seems to be in the range -50% to +75% of original speed. My apologies - Ignore the first bit of the last post.

I do feel it could be miniaturised to use smaller ball-bearings (hollow?) though and with a more sensitive shifter do the same amount of ratio for less weight, albeit with more moving parts. Kind of like a Rolex.

I'm genuinely intrigued by this and would love to ride an equipped test bike. Or read any reviews if anyone's seen any?