Vivaldi looks like a very good browser. It has a lot of features and the most customization I've seen in a browser.
However, the reason it is impossible to use it is its resource consumption. It is REALLY slow compared to almost any current browser. Its ram and cpu consumption is even higher than chrome and it is impossible to use it on a laptop without it consuming all the battery.
Recently, I did a test between vivaldi and other browsers like edge, chrome, opera and brave. In the test I installed in all browsers the same extensions and opened the same pages as well (like youtube, reddit, google, twitter, pinterest, wikipedia, etc).
The result was that vivaldi consumed about 150mb - 200 mb more than the other browsers. In addition, it was too slow, while the other browsers were running smoothly.
The developers of vivaldi REALLY need to optimize this browser. All they do is add more and more stuff to the browser that slows it down.
I would like to use vivaldi as my main browser because of all the features it has and its customization, but it is just impossible.