Just received today, so very much an "initial impressions" preliminary review.
This 3.5" blade is a beautiful monster. Great edge out of the box, and the action is smooth as silk. Rolling the blade out slowly with my thumb, there are absolutely no little "hitches" in the glide that I can feel in many blades. Not that those are ever a deal-breaker, as those will break-in over time, but the absence of any rough spots is a testament to the build quality from Maserin.
Speaking of, the blade is dead center and the M390 looks and feels great for some test cuts.
Aesthetics: I went with the green Micarta and it pairs very well with the wash of the blade. The blade shape and size seemed to lean more toward "work" than "show" to me, and the wash and the Micarta make this knife look anxious to do some work.
Looking at it in person, I could also get behind a mirror polish on this giant hunk of steel and the flashier carbon fiber scales. The classic design elements really give it some flexibility. The back-lock and stud-mounted clip give the scales a minimalist and symmetrical look that I'm really digging.
Carry: as a lefty, I appreciate being able to spin the clip around so easily with the included wrench. The jimping on the blade is pretty aggressive, and can snag and chew on a jeans pocket without a little care. You'll always know a blade of this size is there, but there is no excessive steel in the frame so it carries light for its size.
There is a pleasant, grippy texture from the fibers of the Micarta. Obviously on day one it is too early to tell if they will wick up anything as Micarta-haters complain of, but given the care evident in the rest of the manufacture I don't expect Maserin to have skimped on the resin in either quality or amount. After some hard use, I'm looking forward to the scales having a subtle patina that distinguishes this as distinctly mine.