The question regarding this steel has come up on a few occasions on another forum on this Site. The copy/pasted response below is not from me as I'm totally unqualified on this subject matter, but the author of this blurb is a very, very respected knife-maker on here who adheres to his own experimentations and findings, as opposed to data sheets, etc. I am merely posting this to present another opinion on the matter, not to flame or draw trolls to where it was copied from. Take it FWIW and as you may wish to:
"The Shiro I'm carrying uses M390. I think I had it in a Reate I lost too. It's not great. No better than the S30V in the Sebby I was carrying before that, and that didn't set a very high bar.
I have experimented with the alloy here and have done heat treat trials with it. I don't really like it. It's not bad, but it's not great. I suppose the abrasion resistance is very good as is the corrosion resistance, but it doesn't stay very sharp in real use as well as alternatives such as Elmax. I think there's just too much alloy and carbide for the matrix to properly support a knife edge. Mushy crumbly when I've used it.
I think one reason folks have mixed results with it is because, in my experiments, it was unusually sensitive to quench rate. The Rockwell hardness numbers they show in the data sheet are what I've seen in atmosphere quenches but my testing of the alloy here I got significantly higher numbers with faster quenches. This degree of sensitivity and the variation you will get from one setup to another and from one geometry to another means that the optimized heat treat for it may be illusive and inconsistent. Most volume makers waterjet, heat treat, then grind. That solid cutting edge area was thick during the quench, and it was a nitrogen gas quench in the oven which isn't real fast to start with, so I don't think they're always getting the quench rate that alloy needs. Not ideal for the alloy and would explain why it doesn't perform great in the factory knives I've used.
So, to me, I think it's probably an outstanding material for it's intended uses, but for cutlery I've seen better real world performance out of regular S35VN. People put too much credence in those card stock cut tests and perhaps knives with obtuse edges or subject to light use. I played with it and didn't get the edge stability I want and haven't messed with it again."