@GreyVR not to be combative, but here are my opinions on some of your complaints mainly on why you may or may not need to actually have that information displayed on the computer
First one is that there should be a handwritten note on your slate somewhere with three things on it. These three things do not change on the dive, and need to be memorized. These are your three limits of depth, air, and time. They will come up in the next paragraphs.
Compass with PSI display. I do think that leaving the center line untouched like is done on the NERD would be nice. On the NERD it's obviously much more critical because the center line is the ppO2 readings of the cells, but on OC it would be nice. Even if it is a split cell with both pressures which is something that we've asked about since it came out. Under the compass isn't the right spot, it should stay in the left or right cell of the center line imo.
Now, in my experience, I don't think you need to have the big compass out unless you are actively navigating somewhere over a long ish distance and need that degree of accuracy, in which case I am using a nav board, but to each his own.
ppO2 and MOD. These are not numbers that you should have to see on the main screen of your computer, especially as a recreational diver. These two numbers are showing the same thing for your context, so you need to see either one or the other, not both. Your chosen ppO2 limit chooses what your MOD is, so seeing both isn't relevant. MOD is not something that the Tec mode actually allows you to choose to display. You can't remove ppO2 from the center section, so you can set your ppO2 limit to 1.4 and then it starts flashing at you because you hit the MOD of the gas that you are diving. So the MOD itself is written on your slate somewhere, and the computer is going to let you know when you get close to your MOD because you hit the ppO2 limit that you are comfortable with, so why display both?
The CNS reading isn't something you have to worry about until you get to O2 deco, and even then it's not something that anyone I know displays on their computer. Oxygen is toxic, your body can't handle elevated ppO2's for very long and the higher the ppO2, the less time it can handle it before you have a seizure. These limits are not something you'll reach with nitrox diving without going into decompression so as long as you are diving within NDL's, you don't have to worry about CNS. The computer will still warn you about CNS when/if you hit their limits whether it is on the screen or not. As one who finds that warning, it is quite obnoxious.
Good reading here
Shearwater and the CNS Oxygen Clock - Shearwater Research
Now, slate questions. What are you using, if anything for a slate?
I use two slates on most every dive. I always use a wrist slate like the one below. They're cheap, they are right there for you to look at, you can write things like all of your dive limits on them so they are right there. Again, you are writing Depth, Air, and Time limits. You start with the air limit which is your rock bottom calculated pressure limit. Depth is next which is either the MOD of your mix, the hard bottom, or whatever your planned max depth is *i.e. the top deck of a shipwreck or planned depth on a wall*. Time is then determined by your NDL at that depth.
Also convenient for writing any random notes about the dive because it's always right there.
DGX Underwater Wrist Slate, Multi-Page (Black)
If you don't have a lot of forearm real estate, or are a lefty where both your computer and slate end up on your right arm, then you can mount the perdix onto the top sheet of the slate. This is something that was popularized by Edd Sorenson
When I'm doing a lot of navigation, like in a quarry or something, I use one of these. Draw the map above the compass, on the side you can draw your waypoints as well as your limits. Back side of slate can be any notes you need to write. I take this pretty regularly and clip it off to my butt d-ring.
