This might work in a gym, with the effort returned to 100+%, but nowhere else. Muggles are lazy.

Great idea. Not sure if the easily frightened will use it though.

How do I carry my nightcap tea tray plus my paper under my arm when going upstairs to bed?

Incredibly Brilliant!

Good luck moving furniture, large boxes, and doughnut carts that way.

OK for situations where individuals move one-at-a-time - but sadly, not a replacement for an elevator or escalator. Might be fun to have at home though.

Coming down seems awkward and jerky, maybe some simple friction or compress some air to be used for the next trip up.

If it requires less than 10% of the effort to climb stairs, won't this just make us even fatter?

I don't quite see it. For this case with an independent chair that travels it would be much like going up a rope with jumar ascenders. The person going up is definitely inputting energy with each deep knee bend, and I would say it is roughly equivalent to walking up the stairs. In each case the person must convert muscular energy into increasing potential energy which is the same at the top whether by deep knee bends or climbing stairs. The trip down involves additional work (energy) to stop yourself each increment of descent, much like stopping on each stair on the way down. I am not good at puzzles so maybe I have missed something. However, if the chair and person were balanced by a weight on the other side of a pulley, then the person could move by pulling down on the bars with a low force just enough to overcome friction, and likewise lower himself with a small force again to just overcome friction. Viola! Of course the chair would have to be locked in the down position, or the weight locked. A smaller person could then come to the chair, request a certain lesser weight be attached at the top and ride up at low effort. All well and good as long as the weights available at the top and bottom can accommodate the different people using it. The weights could be transported up and down by a "machine" behind the curtain using energy to maintain the correct weights availability. But hey, the person riding wouldn't have to worry about that.

This is not going to work for older people. It looks to be pretty tough on the knees.