I'm a believer in PE foam and its benefits for keyboard acoustics and feel. I've bought and modded a few Keychron V5's and used PE foam from Keyboard Kustoms and really appreciated it. I was looking for a similar benefit to my new Q5.
After installing this PE foam on my Q5, the sound and feel were improved the way I hoped. However, I noticed key presses not registering on a few keys. I opened the VIA key tester online and noticed a few keys (down arrow, "F", and a few others) either not registering or only doing so after a few key presses or after a hard press. I reopened my Q5, removed the PE foam, reassembled, and all of the keys register now.
After some checking, I’m sure that my key switches are a bit worn and aren’t clicking in fully to the plate, causing they to lose contact with the PCB. Pretty sure it’s my fault - the PE foam just exposed it.
Giving an 4 out of 5 - definitely is cut to match my board, definitely fixes sound and feel, but might impact connectivity if you have loose or worn key switches.
(My setup: Keychron Q5 without a knob, Gateron Oil King switches, force break mod on frame, tape mod on back of PCB, some minor pad updates to stock stabilizers.)