I know that I am overly paranoid but they do the weird user ID thing. It it opt in as they said in their privacy policy.
When you install Vivaldi browser (“Vivaldi”), each installation profile is assigned a unique user ID that is stored on your device. Vivaldi will send a message using HTTPS directly to our servers located in Iceland every 24 hours containing this ID, version, cpu architecture, screen resolution and time since last message.
We anonymize the IP address of Vivaldi users by removing the last octet of the IP address from your Vivaldi client then we store the resolved approximate location after using a local geoip lookup
At least to my knowledge brave do not do anything like this or maybe it is opt out by default. But honesty, I think from now, I will recommend both of them and just let people choose.
Ofc I will try my best to tell people about up/down side of a product. When it come to ungoogled chromium do they still support manifest v2? If yes then it will be also a great choice for desktop.