As an alternative, you might consider using Crank Bros Eggbeaters as well. I have been using them for several years now and like them a lot. I can even stand and pedal now that I have gotten used to them. I was not able to use a "peg" leg solution as I couldn't twist far enough to get out. Even at that, I never release my prosthesis until I come to a stop, so it has caused me a scary moment or two, but with a little thought and training it seems to be easy enough to avoid the issue. The nice thing about the eggs is that the cleat itself is what determines the release angle and the spring tension on the pedal side stays consistent. I have found SPD to be problematic in that the tension is often too hard to get out at a high enough factor to allow me to stand and pedal as well.