I carry and use a BM rescuehook frequently, and have always thought that some Spyderco-style ergonomics would improve the good idea.
The issues that I see with your design are the same ones I have with previous rescue hooks to-date, and that is that for me to use anything on the side which is opposite the strap cutter end, I have to be holding onto a wickedly sharp blade.
The idea, as I understand it, from previous incarnations of strap cutter tools, is to keep the blade in its sheath for such applications and utilize the sheath as a handle. The problem with that is that most people who use strap cutters like these have them affixed semi-perminantly to some piece of gear, so detaching the sheath from the gear is impossible or impracticle.