Listening back and forth I found the ATH-M50x headphones a bit brighter. They seemed like they could be harsh and fatiguing over time, though I did not listen to them for an extended period to confirm this.
The Shure headphones had a fairly even bass extension. Nothing amazing, but balanced and fairly true. By comparison the Audio Technica headphones were thin with deep bass, and seemed to be compensating with a noticeably louder upper bass. On spoken word most voices had a honk, sounding chesty or nasal. The ATs exaggerated mild room resonances making them seem like a bigger problem than they really were on the Shure headphones or on speakers.
I noticed outside noises were easier to hear wearing the ATH-M50xes than the SRH 840s. I prefer the isolation of the Shure headphones, which was much better than this Audio Technica model.
Audio Technica does a good job with build quality in their products, from their cheapest to their highest quality models. The ATH-M50x headphones looked sturdy. The detachable cable would make it fairly easy to replace for those who put a lot of wear and tear on wires.
At nearly $50 less the Audio Technica ATH-M50x headphones made some noticeable compromises to reach the price point. They are certainly usable and – like most transducers – one could learn how to listen reliably on them with enough time and experience.