Vivaldi is really good visually and has good features. But the fact that it is closed-source and may not have uBlock Origin is a bad thing. I used to accept black boxes a long time ago when I was starting to write my own programs, but I have now seen all the bad things coming from closed-source applications that I am very careful now.

It's not more a privacy risk than other applications, but you cannot check or know whether it's the truth. And what happens when they start to fuck me up because it's "free" and I have to spend a whole week-end migrating to another browser because the CEO needs more money and starts to do weird stuff with his project?

I may over react, but I have seen bad behaviors for more than 20 years, and I am careful now. If I don't use it, I avoid 48 hours of technical support trying to find an alternative. Also it is based on Chrome which makes it more restricted for the plugins. Yet another bad thing that I can avoid right now by not using their product.

A summary would be: it's good (good), but it's based on Chrome, it's restricted, I am dependent on yet another company that will switch sides because it technically has no clients (it's free), and it's closed-source.

Last but not least, they had a thing in their terms of services which said that they could close your account without warning if you didn't behave elsewhere on the internet. Another red flag.