I just received mine today (2 days after ordering in the UK) for my M4 11in Pro.
Initial thoughts are fairly if not unreservedly positive; it’s a compromise and a well-designed and worthwhile one:
it really reduces contrast on the OLED display, which would be a shame except it is very easy to install and remove, with no residue, and for notetaking etc it’s tolerable. More noticeable than the nanotexture glass, but not permanent of course
the feel of writing with a fine (0.7) metal nib on a toothy surface is really great and much better than the default
it’s a better solution than the paperlike I had on my old 12.9 m1, mainly because it’s removable and gives less of a rainbow moire
I’m a bit nervous that I’ll forget about the metal nib, take the protector off, and put a scratch across the screen with the RPP nib…
I’ll probably leave it on for work days and take it off in the evenings if I can be bothered and am watching movies on my iPad. I use it for both and it’s a serious productivity device as well as a media consumption one for me…