It seems to me that Google once had wonderful regular expression searches. That all got blown up when they introduced "Google+", thereby destroying REs.
Could you explain more about this "Basic" free tier? When I go to https://groups.io/static/pricing, I see a free 30-day account, after which it becomes $20/month. You're not the first person who has said there's a free plan at groups.io but I don't seem able to get one myself. Have their plans changed recently?