An onside kick is usually as likely to succeed as a Hail Mary in professional football. It's a last resort for a reason, after all.
The Falcons must not be big on analytics, because they beat the odds and recovered two onside kicks (technically three, if you count the first that was called back due to penalty) on consecutive kick-offs to stay in the game against the Saints. That is almost impossible, but they pulled it off.
Here's the first that led to the Falcons kicking a field goal at the two-minute warning to bring them within eight points of New Orleans after trailing all evening:
And here's the second, recovered after the previously-mentioned field goal, that gave Atlanta a chance to drive down the field and tie the game.
The Falcons were ultimately unsuccessful in their quest to tie it up, but Younghoe Koo has certainly demonstrated his prowess as an onside-kick specialist. I doubt we'll see this level of success again this season, and perhaps not for a while yet.