I have the XM4s and they are very good. As far as I can work out there isn’t a great deal of difference sound wise from the AirPods Max, as there’s a limit to the amount of information you can send via Bluetooth. They do come with an audio cable which may improve sound quality, though I’ve not tested this as have better wired headphone. The noise cancellation is very good, probably on a par with Bose and much better than my AirPods Pros, and they are relatively light without too much clamping force, which is useful if you wear glasses. They also come with a decent hard case and have usb c charging which is a useful feature.
The two downsides are the built in microphones are pretty rubbish and they are on the base heavy side, which is fine for general listening but I wouldn’t want to do any mixes on them as even with the EQ in the app, you can’t get a flat response. From what I can work out the only real advantage over the XM3 is fast Bluetooth device switching - by default I have mine connected to both my iphone and iPad at the same time, which is useful if you get a call and are listening to something on the iPad. Finally they do have an on/off button, unlike the AirPods Max, and fold a bit more if you want to travel with them.