During winter months, especially, my early-morning erg sessions are done in a rather dark room. It's really nice to be able to see the display so well. My aging eyes appreciate the backlight.
Caveat - I have no experience with a non-PM5 monitor. Maybe those are easy enough to read too.
When I was buying mine, new, I went back and forth between model D and model E. In the end I went with D, and am glad I did. I put it together before sessions and separate it after, for every session. The halves / sections are rather lightweight (especially the rail / seat section) and easy to set aside. Being closer to the floor might have advantages too, for an older person like me. Not as far to fall to the ground.
I understand model Es are even more ruggedly built (if that's needed) and taller. Maybe good traits for certain situations.
Good luck regardless of your choice.