On desktops I don't see any reason to use Brave, but on smartphones it's a different story.

Advantages of Brave on mobile in comparison to Firefox:

- Single package with add blocking and HTTPS upgrading

- Better handling of offline cache

- Those little PIP clouds to disambiguate a tap

- I always understand how to long press to show context menu instead of selecting

- I believe scrolling is smoother on Brave

- I prefer card/tab layout on Brave

- Less crashes

Advantages of Firefox over Brave on mobile:

- Same browser I use on desktop - helpful with Firefox account and it's FOSS

- I can disable JavaScript and images when I'm on severely limited connection like right now

- Extensions

- I like text search better

- Better location bar search

- Usable reader mode

Now saying all this I would like to have a pure HTML browser, at least for bad mobile connections. It would be lightinnig fast and would show me offline version first and upgrade to more recent version if needed or it was downloaded after all. It would be like a permanent reader mode. So my font, my colors, my line length, no obnoxious position:fixed bars. One of the things on my to-do list.