Even if your device is not listed, it is still supported. Every phone launched with Android 8 or greater support project treble. Thus, it also supports gsi.
DSU, do you have a OnePlus N10 or N20? It does not work. If it works on your OnePlus, please provide the extra/special steps you took other than tapping the app and selecting a gsi, then rebooting. Nothing happens on boot. No gsi. Just boots normally.
Both N10 and N20 do not support DSU because they launched with the Android version less than Android 12.
But you can still install GSI with the traditional method.
Check you VNDk version with this app and I can tell you which gsi's are supported by your device.
No, it's not at least in my case. Actually GSI Lineage is a little bit faster due to less bloat than stock. But performance could be different for different devices.
Note: I experienced some bugs but all of them were easy to fix.