On Mobile (using Mull) the PDFs are completely pixelated and simply dont render more details. Even after zooming in it takes forever.
Meanwhile on Desktop (Librewolf, Firefox, … on Fedora) it seems a bit slow compared to Okular, but it is very fine.
Just tried it, works very well and fast but I think I prefer MJ PDF also because it runs on hardened Chromium so less RAM etc.
Also MJ PDF has a dark mode, inverting black/white on texts