Bought a Protec case for an alto sax and thought this would make a useful additon to free up hands when there's a long walk to the bandstand. In practice, the backstrap has proved its worth many times over, either slinging the sax over one shoulder for a short walk, or using both straps for a longer route march.
Slightly fiddly to fit, but not a real problem, although the instructions could be a bit clearer to make sure you get the strap on the right way round first time.
The only improvement I can think of would be to provide some way to tidy the straps when you're not carrying the case on your back. They dangle somewhat irritatingly - I may have to improvise something with a length of Velcro or similar.
**UPDATE** After several years, the backstrop was showing signs of wear - mainly fraying along the seams and an occasional tendency for the plastic clip to unhook itself. I decided to buy a new one (two actually, as I have one for my tenor, too, and it was wearing out as well). Interestingly, the new version has taped seams, so it appears that Protec have discovered that the fraying is a design weakness and they have addressed it by taping the seams. Excellent!