Long time lurker here, these are just my first impressions as an newcomer to wireless headphones with noise cancelling.
Received mine yesterday, comparing them to a set of PX7's I have on loan;
For my tastes I enjoy their sound a lot more than that of the PX7. As with the PX7 they have overbearing bass (for my tastes), but it is not the same type of bass (for lack of a better term). Once dialled back (and I'd rather dial back than have to try and add) a bit they sound very musical. Not as muffled and fatiguing as with the PX7.
Observations;
To get LDAC working on my Sansung Note I had to enable Developer Tools, adjust the bluetooth settings and then afterwards enable the slider under the settings of the paired bluetooth device. It was missing at first.
The highest LDAC setting stutters. But this seems to be a known android issue on some phones.
I like the materials used on the PX7 more. On my head the PX7 sits more comfortable. The XM4 has slightly shallower cups, and they get slightly uncomfortable after a hour or two. They have less clamping force and a overall looser feel, I would probably prefer the PX7 for commuting, but I have no interest in buying them due to how they sound.
LDAC is not available when using multipoint pairing in the app. Mine defaults to AAC.
Unlike the PX7, I cannot listen to music on my computer when connecting via a USB C to A cable (or C to C on my mobile phone).
Negative;
I'm experiencing stutter and lag when paired with my Samsung television, with or without multipoint pairing. I do not experience this at all with the PX7. I have found at least one other user on Youtube with the same issue on a LG tv.
Everything else seems great, especially the noise cancelling, app and sound signature, but if I cannot sort the television connection issues, I might return them and try the Aonic 50.