So, I've had the speakers for a bit more than 2 weeks now. My impressions evolved quite a bit after the honeymoon phase.
These are really nice speakers, and I do think they punch above their price point and size. But you also need to be aware these are pretty neutral speakers (at least to my ears), which makes them pretty agressive in the treble if you're very sensitive to it (like me).
I ended up doing two things to improve the sound for my tastes: plugging the backports with foam to reduce bass emphasis, which made the overall sound clearer, and play with the app's EQ to increase bass and mids and reduce treble. +1dB up to to the 4 kHz band and -1 dB from 8 kHz. Not a big change but it sounds much better to my ears now - quite a bit more muffled, but also less fatiguing, and I can now listen to the speakers for longer. The slight bass boost makes the speakers sound warmer (which I like) and the boosted mids make the sound detach more from the mix, which is also nice to me.
So overall pretty happy with these M60, just have to keep in mind these are not warm speakers unlike what I'm used to.
(for reference I've been using a Sony WH-1000XM3 - very bass-y headphones -, a Meze Empyrean - warm headphones -, an HD 58X with an Alex Cavalli CTH tube amp - so pretty warm as well - hence my preferences I guess)