Additional downside I experienced with .io in the past was the non existent support or urgency when it comes to technical issues.

Some of you might remember the incident with .io back in September, 2017.

Since then, ownership for .io passed hands and landed at Donuts who is also managing .org so I assume it's in a better shape now, but lesson was learned.

If it would be up to me again, I would push to use .io or any other vanity domain for marketing only.