"Traditional" nitrogen fixing bacteria make their way to specialized nodules. Basically this is because the nitrogenase enzyme is incredibly oxygen-sensitive, and it's quite difficult to shield the interior of the enzyme selectively against oxygen (oxygen and nitrogen look awfully alike from a physical perspective). Inside a nodule, the plant maintains an anaerobic condition that protects the bacteria from oxygen, which for some reason plants like to produce. Added efficiency is critical, because nitrogenase is already a VERY inefficient enzyme. 16!! ATP + N2 -> 2ammonia + hydrogen! There are often enzymes in these bacteria whose purpose is to recycle the wasted energy from the hydrogen produced from nitrogenase.

And if you think there's a way to improve the efficiency of nitrogenase, that would be really welcome, since nature seems to have evolved it only once.

Upshot, without some serious plant engineering, at the very least using aggressive husbandry techniques, it's likely this tech will hit a hard ceiling in terms of usefulness.