As someone who just transferred 20 years of old complete email accounts out of my old Opera 12 onto a shiny new Windows laptop, is the mail client dead still? Despite the fact that they accidentally showed IT WAS IN THE SOFTWARE AND WORKED when it leaked out once?
Because I use Vivaldi but don't really care about most of it (the best thing is that I can re-map keys so that new tab is Ctrl-N and not Ctrl-T) - but I'm still desperate to find a mail client that's actually usable in the modern age. That Opera 12 is still my client of choice is very telling.
Otherwise, Vivaldi is just Chromium with some knobs on to let you have start screens and themes and stuff I never use.
They've changed the icon at least four times to my knowledge, and each time announce it like it's some amazing top-of-changelog item.
And they've recreated every one of Opera's classic problems - "we must change the user agent so people are aware Vivaldi exists" followed by a hasty (and so predictable that even I called it) retraction when they realise that sites still just break if they don't know what your browser is based on, then trying to suck all my data into unrelated cloud services, etc.
I don't use the mobile browser, I see no reason, but the desktop version is convenient as it's basically Chrome, with Chrome extensions, but stored in an entirely separate profile so it doesn't interfere with Chrome proper. It's like a giant version of incognito that I can use Chrome for home and Vivaldi for work, and they both work and do everything but are both unrelated.