For now! But you probably read about the territorial dispute at the end of the article. Totally possible that the British government won't be controlling that domain at some point in the next 10-20 years.
The resulting arrangement would virtually certainly be something like Tuvalu and .tv. Nobody is suggesting that they go into a Freenom-style domain mess like .ml and a few other domains (which some countries decided to just give away for free).
But if you choose .io, you're gambling on the future of your internet property in a way that the owners of traditional domains like .com simply don't have to worry about.
What if someone decides to start a media campaign for divestiture of .io domains? It's not particularly likely, but it's a risk to weigh against the benefits of a cool domain.