I built one of these some time back, the only problem I found was that over a period of time (months), the knots at either end work their way out, unfortunately, because the angle between the knotted cloth and the ribbon is quite steep (and has to be to stop the knot slipping), the weave of the cloth tends to weaken substantially with the eventual failure of the material (I tried ripstop and canvas). I have two personal requirements for "kit", the first that it is cheap, the second that it will last. Consequently I want something a little more permanent.
Although I don't have access to a sewing machine, I really do like Neil's design, and I think I will probably give that a go (with some minor additions for comfort).
However, I'm also trying to get away from the fraudulant b*******s I work for, so am really short of cash at the mo. Will probably do this in about 6 months time when I have sorted out my life.
Greg.