Discussion in Farm Progress.[1] The maize plant in Mexico requires a 9-month growing season, so it's only useful in near-tropical climates. Work is progressing to see if the trick that plant uses can be adapted to something that grows faster.

For a plant to fix its own nitrogen carries an energy cost. So the plant grows slower. There's a tradeoff here.

[1] https://www.farmprogress.com/biotechnology/nitrogen-fixing-c...