Chrome will block add-ons outside the app store
The reason I'm talking about is that add-ons like [url=https://vivaldi.net/en-US/blogs/featured-blogs/entry/restoring-the-old-opera-12-space-bar-behavior-in-vivaldi]this[/url] will be lost forever and I want Vivaldi to not do this.
Edit: I didn't see your link at first. I can install the userscript to vivaldi without problem.
Unless chrome is blocking tampermonkey, I don't see it a threat at all.
Tampermonkey has been handing userscripts since forever, and is very popular on chrome.