So I have the XM4's and I've listen them for about 20 minutes to make some first impressions:
First thing, YMMV, but they fit MUCH better than the XM3's. They are not the most comfortable TWS I've ever wore (Damn you MT. Damn you all to hell), but they are more secure and I can get a better seal with the foam tips more consistently. For my admittedly large ear holes, they sit flatter than the XM3, and I would say they actually are in my ear a tiny bit shallower than the XM3. However, they are still rather large, they're no Galaxy Buds Pro.
The case is a little more than half the height of the XM3 case, about 25% less long, and very slightly less wide. The case opening is pretty loose, but open it far enough, and it clicks and locks open. Much more portable.
So the bad news first: If you use the app to get the optimal "wearing condition" to get the best seal to have the most efficient ANC, these things are bass monsters. Also, the mids are weirdly tuned out of the box, and the treble roll off is considerable. They are very dark, very much the Sony house sound.
However, the EQ does work pretty well. It's not the most granular I've ever seen, but it does make a difference. This is the settings I'm currently using based on the measurements that SoundGuys posted on their review to try and even out some of the peaks and valleys.:
It tames the booming bass quite well, and makes it sound much less darker than before. I'm still tweaking things as I hear more. Again, your YMMV dependent on your listening preferences.
Overall, the tech and form factors are so much better than the XM3. Sound wise, due to the improved fit, I actually like them even if I have to tweak the EQ to tame the bass.
Edit: Also a tip for those that are getting it: Update your sony headphone app. The fast pairing didn't work for me at first, until I updated the app.
Edit 2: I ended up boosting the 6.3k and 16k to +2 and +3 respectively. But I think for me, it's the 6.3k is the one I'm going to be tweaking the most, it's the one that is sounding "off" for me dependent on what music I'm listening to. Haven't figure the best level for me yet.