Sadly, they don't list a comparison to my personal favorite: Wire. Yes, Wire requires an email address but Wire will accept a single-use/burner ProtonMail account as the linked email address. VoIP call quality with Wire is the best I've used and I can use the app on a desktop browser as well as my mobile devices (and the app is available via F-Droid). Contacts are managed in your Wire account (no attempt to connect to your phone's Contacts provider). They do make it difficult to find the signup for the free personal plan though: https://app.wire.com/auth/#setaccounttype