That's not really what "being the product" is commonly recognised as.

Vivaldi go out to their customers (that's not you) and say "We have 1000 suckers who have downloaded and use our closed source, Chromium cloned, browser. We can serve your website as a bookmark to them, or add you to their search engine list if you give us $x."

Since you are not their "customer" (that's the people paying them to appear in your settings) what are you? You are the "product", you are what Vivaldi is selling.