I have a one of these on a 50's Lenton bike.
Mine is set up as a 4 cog rear, with a suicide
shifter on the front.
It's a project and I'll probably end up modifying it
with something that works better.
As stated previously, I think it's a pretty limited
market, because most of the bikes they came on
(at least here in the USofA) are either wall art
or gone to bicycle heaven.
E-bay gets a world wide market though, so i could
see where they might be just the thing someplace
where there are more bikes left that came with them
as original equipment.
I'm far from expert in the e-bay marketplace.