Looking to invest in some new cans. Anyone using or know pros/ cons about AKG's K712 Pro (or K612 Pro) studio headphones?

I have not listen to either but I would be hard pressed to pay almost $200 more than I paid for the Q701 for the K712. Not that the K712 would be bad and now you get a bump-free headband, a coiled cord and bag, maybe that is where the extra $$$ go. Well that and maybe slightly better low end but the Q701 are good enough for me. I have had AKG headphones for decades. I liked my AKG K204m but they finally died after years of abuse. Got the Q701 on  15% off sale on top of a price match. It was a good deal. Best headphones I have ever owned. I am sure the K712 would be just as clear and detailed as the Q701. They will also suffer the same issues that all open air designs have such as leakage and not being suitable for noisy environments.

I use cans mainly for critical listening, checking tracks or mixes. The K712 pro is designed for mixing / mastering, open air & leakage wouldn't be an issue.
I'm curious how accurate & useful they'd be for m/m purposes. 
If the quality & price were right I may consider them to use along with or instead of my ATH M50's.