Never said a good variable does not work fine. Used many myself.
Re: eye doctors - they seek to bring vision into sharp focus. Not magnify.
Mackay - seems JB spoke good things on the durability of the MK IV. No doubt glass would be less than an S&B optically. I was never impressed with the M8 10x but it worked reliably - the FX 12x was an improvement over the M8 version
But with the higher price tag I would hope the MKIV was better than FX glass. Not compared SxS.
