To me, Z-system is a simple sidemount system, that breaks multiple fundamental tech principles in an effort to work like back-mount. That isn't a dive determined necessity (other solutions exist) - it is an agency dogma mandated necessity. It has no need to work like back-mount, it isn't back-mount. It is workable... but it isn't optimal - not if the diver respects the principles of minimal failure points and K.I.S.S in respect to configuration and procedures.
I just don't see the benefit of compromising a majority of important principles in order to effect one single principle. Especially when that principle ('from the mouth' donation) is of much less critical nature.