I have been using Vivaldi for about half a year and so far it is working well for me. Originally moved to it due to it's privacy features, but finding other areas quite useful too such as workspaces
I use Vivaldi as well but every time I update it I need to change one of it's internal JS files to remove one UI restriction that annoys me: I use two vertical tab bars, one for showing all the tab groups and another for showing the tabs inside the selected group. For some reason Vivaldi limits the width of the two sidebar (combined) to 330px, which is too small for my tastes.