The display can definitely be turned off. That is how mine is at the moment.
I went from a Power Plant Premier to a P5 to a P10. I certainly didn’t need the P10 for the “load.” But I trusted those who were telling me that the P10 sounded better.
The Premier to the P5 was a big jump in sound quality. In comparison the former had a signature that the latter did not, and the latter was more transparent and dynamic. There was a jump between the P5 and P10 of a subtler nature. . . more refinement to the sound is perhaps the best way to describe it, more precise tonal detail, more ambient information, a bit more dynamic, a sense of ease that headroom gives. The P10 unquestionably sounds better and I wouldn’t want to go back to a P5 if I didn’t have to.