I couldn't see the counter-weight. A counter-weight matched to the sole user (able-bodied take the stairs) would make a huge difference to the muscular effort involved in getting up and down.

This seems to be about halving the strength requirement because you can use both legs on every step, while also eliminating the balance and coordination requirements of climbing and descending stairs. Maybe that is all that is needed if some-one has had a stroke and falls just short of being able to use stairs. But I don't see it buying much time with a progressive condition.