Pros: Portable, bluetooth, apt-x, headset, NoiseGard
Cons: difficult fitment, not great sound
Unfortunately not the be-all-end-all.
After seeing and hearing the MM450X at the Frankfurt Airport I though it had it all and could do it all: Bluetooth apt-x, noise cancelling, bluetooth headset, wired passive, talk-through, compact and foldable, easy to recharge, and with decent sound.
After some ownership i've found that it's a bit of a compromise and the perfect do-it-all is still yet to be made.
Features: Gadget-wise the MM 450-x has it all and performs. Apt-x is noticeably better than standard aac A2DP. Headset microphones are excellent as they noise-cancel. NoiseGard works, though not as well as the QC15, and nowhere near my Ety's, but it would be more fair to compare them with the similarly on-ear AE2. Perhaps next time I'm sitting next to someone with one i'll ask.
Talk-through is also a great feature when sitting next to coworkers or responding to FAs - pulling deep IEMs out and back in is a hassle.
The MM450 also wins in usability - buttons are easy to find and pleasant to press, and the ability to use BT without NoiseGard is useful.
Battery life is suitable - about 20hrs in wired NoiseGard mode is more than the amount of flying you'll want to do. 10hrs in BT mode is enough for a long day of work where you probably don't need NoiseGard, and 8hrs with BT and NoiseGard... I'm not sure where exactly you'd use this - on a train/bus?
Comfort: the MM450X disappoints a bit here. Most on-ears now have soft foam pads. The pads on these are definitely on the hard side. I'm going to try to fit soft foam pads from the K450.
Portability: Not quite as compact as the AKG K450 or the Sennheiser PX100-ii but still better than carry a full-size Hp around...
Sound: This is the biggest let down. For something with an MSRP of the HD600 I expected better. Highs are detailed, but mids are dry and grainy. Bass is there but lost in poor fitment. I'm hoping the cushier K450 pads fix the sound.
With NoiseGard on the bass is boosted slightly, but this is in a quiet environment.