And as a mechanic,I can tell you if you use mechanical blades long enough THEY WILL FAIL at some point.
The funny thing I have found with reasons like this for not using a mech head is that this same argument is never used against putting a drop away rest (which seem to be universally loved) on your bow even though it is a far more complex design, has to stand up to much more repeated usage and therefore has a vastly greater chance of a mechanical failure. A mechanical head after all is just basically a simple hinge when you get right down to it. And for me it only has to function properly as a hinge once. That being the case, I like my odds. And through about 8 different designs and many deer I haven't seen one fail or fail to open. As for the latter I don't see how it could fail to open unless I glued or tied it shut. It simply defies the laws of physics.