as everyone said, they don't work as well as they used to. But I'm pretty sure they can help you rank in other search engines, and with google's slow but sure downfall you gotta look into alternatives, and stuff that worked 15-20 years ago in google (keyword stuffing, EMDs, exact match anchors, etc) are probably now the thing in lesser SEs...
I'd say go for them! As long as they're regular price ($10-15) you won't lose anything but you might have a lot to gain in the coming years... But I think there was an issue with .io domains, I don't remember what it was (something about jurisdiction or country-related issues, I really can't remember, but someone had posted this in the forum a few weeks ago), so I wouldn't go for .io personally. But .coms are fine....