I had the MCDU (older version) of flight deck solutions and the PSONE screen inside.
When the MCDU was built in into the cockpit I had reduced brightness on the PSONE screen because the viewpoint or viewangle on which you look at the screen is low. This means you are actually looking from below onto the screen. When I removed the MCDU and looked at the screen at a 90 degree angle the brightness was much better and when I moved my viewpoint even more up, looking from above to the screen the brightness improved.
So what I did, I installed the PSONE screen upside down into the MCDU and rotated the screen in the display settings with 180 degrees.
Like this the brightness is much better when the MCDU lays down in the pedestal.

Thanks Peter for that tip!
I haven't check as yet quality of PSONE display - had no time but definitelly I will use your suggestion.
Hopefully soon I will have more info for you guys, as my I/O project has moved forward.