This renders heavy PDFs much, much, MUCH faster than the apt version of Evince and xreader! By far not as fast as MuPDF, and the UI isn't as good as xreader's, but the feature-set is there from what I can see!
It has link previews! Really handy for reading scientific papers. Feature-wise it seems like the best pdf viewer I've ever used. Plays well with system themes too.
Flatpack version works okay. A little slowish in my VM, but could be an artifact of the VM. Can't open PDFs from an SMB share. get "Error while getting peer-to-peer dbus connection: Could not connect: Connection refused"