The big ones for me are a cover/replacement for the fabric face gasket, prescription lens inserts, and for long play sessions a fan insert for the headset can be a nice to have, but I don't run mine all the time since sometimes it's just adding noise. The face gasket has probably been the hardest thing to get right, since a lot of third-party ones either don't have enough padding, or are hard to swap in and out, so I kinda prefer having a full extra magnetic insert so I can easily change between the original which is most comfortable for me, and something else that I'm less worried about sweating all over for more active games.