I think they're really focusing on performance customization with this one and only offer a little more visual customization out of the box, while other browsers offer that through themes and add-ons. I think you could maybe achieve the same thing in other browsers if you know how to make themes for them (there are usually nice docs for that). If you only want visual customization, that might give you more options and control over it than Opera GX, which seems to focus on CPU and RAM limits so gamers can use as much as possible of those for their games.
I've recently seen people switch away from Opera because of their predatory loan schemes in poorer countries. Some of them have ceased, but the gist is that they have offered apps in the Google Play Store in the past (OKash, OPesa, CashBean and others) that advertised good loans, but what you got in the end were loans with interest rates in the 365-876% range, offered for 15-29 days. Failure to pay them back resulted in threatening all-caps SMS sent to the debtors. These rates and day limitations were in clear violation to the Google Play Store as well. They did this because they didn't make enough money off of the browser.
They deny this, of course, despite a lot of evidence..