Just received my ZT 620CF. First impressions - great Emerson-design ergos! It fits like an Emerson, which is one of the reasons I bought it. It !flies! open with the wave. This is the fastest and easiest opening waved knife I have tried (including all my actual Emersons and a couple of spydercos). Fit and finish are top-notch, solid lockup, centered blade, no blade play either open or closed. The polished CF scale is slick to the touch (unlike peel-ply CF used by spyderco), but grip is very secure because of the ergos / handle. I don't have one on me right now for comparison, but the ZT feels heavier in hand than my Emersons. Definitely feels like a solidly built, sturdy knife. This is my only ZT but my understanding was that ZTs are on the heavy side. All my spydies feel much lighter than either the Emersons or this one. Not a bad thing necessarily, but different.
Have not tried cutting anything yet to try out that fancy super M390 (that'll have to wait until I get home from work), but seems sharp and the blade is thick enough to qualify as heavy duty, so this is not a FFG slicer like a Para2 or Manix (sorry for the spyderco comparisons, but that is what I have most experience with).
All in all, I like it. If you really want an "upgrade" from 154CM, either this or the 620 in Elmax seem like good options. All these are great steels though, so to me the overriding factor is execution of the Emerson design.