while I don't think I would run a square shaft in the back, I would (and have) run one in the front. I got spoiled and got a round long travel shaft now, its nice for our dune runs.
A square front shaft works well for what it is, if you don't spend some time getting it on square it will suck, but if you spend some time on them they work very well
I never had mine bind on me, ran it for 3 yrs or so. dunes rocks snow trail rides, it was fine.
Rear shaft does not need nearly the amount of slip the front does. I use a stock slip yoke on my rear shaft. I have never used anything but a stock slip yoke. Hence I dont' see the point for square on the rear.
