Quoted from Pinwizkid:

I bought one, used it once, and immediately sold it. I lifted a Whirlwind up a flight of stairs and thank god someone was there to help me otherwise I would have dropped both the machine and the Escalera down the stairs. It feels like the thing is going lose grip and fall the entire way up - very anxiety-inducing. I couldn't negotiate getting over the top step properly without shifting the weight of the machine in a direction that I was positive would cause a disaster (so again, thank god I had a buddy there to help lift up the final stair the old fashion way). Maybe I'm just super weak/out of shape, but it destroyed my shoulders and upper chest. I was sore for days after using it. However I will admit - my back didn't feel a thing!
Sorry to be so negative on it, but after reading all the positive comments here, I figured I'd play devil's advocate. Looks like it was just me who sucked at using it!