When I was still active with the Mountain Rescue team we used to use the HARE which was spot on, I have never liked the SAGAR becuase of that strange 'T' piece at the top.
The Donway and the FernoTrac are fine, but as Kev says they are not practical unless you are providing soley a medical presence. I have a Kendrick in my kit bag, and although I have never used it in anger, it is a spot on bit of kit that is simple to use and is small enough to actually be practical.
The only draw back with traction splints, in my experience, is often there are lower leg # as well as the femur#. And you are not supposed to use traction is there are tib/fib# although I have watched a BASICS doctor do a double femur traction when the patient had bi-lateral tib/fib# as well.