The material is ok and acceptable, but it is obvious that it is not top quality. It will work for a while (maybe a few years), and most certainly wear out.  The size is ok for a curving staircase, as the one I have with 2 curves, although not a perfect fit.  The description of the treads stated they do not slip. Possibly that is true if you Do Not Walk On Them!!! Yes, they move, and must be pushed back to proper position, but the movement is not extreme.  Three star review means they are only "Fair" and passable for the purpose needed.