Clean and workable
If I were able to post a raw audio file right here on the Sweetwater review I would. In lieu of that, I'd say the M80 is pretty good and getting there. Without the B pole and subdued high E pole (as per factory specs) it has a fairly balanced sound, not mic'd, piezo, or electric, but perhaps all of the above combined.
It's hard for me to convey in words what it sounds like plugged directly into a decent audio interface and recorded uncolored, but it's not twangy like piezo, although it has piezo sonic characteristics without the brittleness.
My Martin OM-1GT is neither boomy nor boxy, so I'll report that the M80 does not introduce audio artifacts but tries very hard to represent the instrument accurately. Room for more R&D for sure, but the M80 could be tops for a while.
It's a hefty investment no doubt, and all the samples I heard on the internet before purchase were colored with an amp or preamp, showcasing a player's skill or band with the M80. Raw is probably more appropriate. Thus, trust me when I say it's good out-of-the-box and tonally clean and workable. From there EQ and effects can make the guitar shine.