Right now it shows odometer, but I would rather see a digital speed number. 2010 GLK 350
Changing it with arrow works but doesn't stick around.

 

Weird that it doesn't stay on digital MPH once you've cycled to it using the arrows. For my 2014, it's the first option on the up-arrow after odometer and it never disappears unless I cycle to another display option. I go weeks without looking at the odometer...

 

When you open the door it will show actual mileage to prevent fraud in selling. If you had it on another screen, it should show that screen after startup.

 

Yes, this is the only time it deviates from the chosen display. Should have been more specific.