Taco Mama is a regional chain with a formula that works well enough to keep expanding. The tacos are inoffensive, the ingredients are fresh enough, and the whole operation runs smoothly. None of that is a reason to go.
Nashville has Alebrije doing something specific and rooted. It has options that reflect an actual kitchen with an actual point of view. Taco Mama has a playbook.
A Southeast taco chain producing the same meal in every city it opens in. Not bad. Not the point.