I wouldn't buy it again!
Shortly after I purchased the premium service for a year, my Floorp internet browser no longer starts when the add-on is activated (I've already tried it with a completely new profile and a new add-on installation)!
I contacted support, but they didn't respond. So, unfortunately, I wasted my €24!
In addition, or rather, it happened (it's been resolved now anyway, since I can't use it anymore!), the add-on itself doesn't remember that I'm a premium user. You have to log in via the 1vpn login area and then make sure that cookies aren't deleted from the site. This way, you have a chance of still being recognized as a premium user even after restarting the browser. This works, though, even though I don't delete 1vpn's cookies, and only for a short time.

Update 11 days later:
It's working again now, even with Floorp.
However, I find the manual login process and the requirement to save the 1vpn cookie cumbersome.

PS: I do like the fact, that I can pay with cryptocurrency, including Monero.
And when the service works, it's been very good, stable, and fast so far.