I wanted to use it to have Chrome convenient experience with tab groups (Chrome is better in that, but don't support multiple search engines and other cool functions), but I can use it only on desktop where I don't need tab group really much because I already have list of all tabs when browsing current tab, and can't on Android where I really needed it. Also realization of tab pinning and tab containers is not very convenient. And creating new tab button is (only) on bottom side of page which is not convenient too. Also I always forget about tabs tree and start using native top menu, and tab tree doesn't even (only icon like in chrome mobile groups maybe) copy there.
P.S. Also with 100+ tabs Firefox crashes several time a day, but I'm not sure that's just because tab tree