The writer is proposing Vivaldi, a closed-source browser, as an alternative to Brave, which is free and open-source. I think a better alternative would be Ungoogled Chromium.
Sure, but Firefox uses a different engine. On my systems, I always have both: a Mozilla-based browser as primary and a Chromium-based browser as secondary. If a site doesn't work on one, it'll work on the other.
I'm against ungoogled-chromium. I used it for a while and it feels like someone took a sledgehammer and smashed up all the Google parts without cleaning up afterwards. I stopped using it mainly because of security concerns.