Softer than FR4, but not nearly as soft as polycarbonate (PC)
This plate replaces the stock aluminum one. I found it sounds and feels good with very few switches. I recommend the 'white' model only if you desire greater LED shine-through. Otherwise, go with the stiffer FR4 plate, which is more versatile with switches.
Also, I suggest waiting for a reduction in price. $25 is too much.
i've learned a lot about keyboard customization since i got my barebones sense75 in july or so and i wish i knew that changing the plate would have made the keyboard sound SO much better - i was new and just didn't know! so now i'm annoyed that i didn't have the choice of plate to begin with when i was buying the keyboard- it would have prompted me to read up more on what the different materials do. anyway, live and learn, replace the plate.
Never used a POM plate before. Prefer the sound of an FR4 plate tbh, but I wanted as soft a plate as possible with how pingy the stock sense75 barebones is.