Hello Jaycat.
I happen to have a Highpath swing crank (the 'Pulse' type) in my shed. It was the first thing I tried after I lost my left leg, as it seemed like a good idea.
Didn't work too well for me. A combination of what I've previously banged on about (crank shortener, pedal extender, Gravity dropper) did the job better, in my case.
But the principle is certainly good. It's yours if you want it, for the postage (a few quid I would guess), but it's only for a left-hand crank.
In fact it CONSISTS of a left-hand crank, shortened by Highpath, and then drilled to take 3 threaded positions for the pulse crank itself to sit in, so you can have it at full stretch, or less, or less again.
I'll send you a pic if you think your left leg would benefit - wouldn't work on the right. You will need to buy (if you haven't got) a crank removal tool (about a tenner from Halfords), as it is for the sort where there is a square tapered hole which the crank is pulled onto in the tightening process.
Two final things: one, you don't need a crank shortener with this one, as the crank itself is already shortened.
Two, other people do make crank shorteners to similar designs, and they do tend to be way cheaper than Highpath's.
Alright, three things: you can borrow my crank removal tool!
Allen.