They are central Texas tree. Their range goes into Mexico , New Mexico and the big bend. I have heard their Zone hardiness is Zone 8 but the range map suggests more. Maybe it is a different species . Dave's Garden says Z7b

Yep it is more of a central texas tree. I don't think low temperatures in Lubbock would kill it, but the branches can break pretty easily when weighed down with ice so they might me an issue

So more or less give it some winter protection to keep the branches from breaking?

The main warning we got when planting TML on the north side of Dallas (8a) was about occasional flower loss because the buds set in the fall. We've had one in the ground for several years without any die-back, though has only been flowering the past two which were not particularly harsh ones.

We had the Sophora worms/Tent caterpillars (Uresiphita reversalis) for the first time this year, but they devoured our little Baptisia and never made it to the larger TML on the other side of the house.

I get those bugs every year here in the Dallas area. Have to keep a real close eye on it and be generous with the poison, unfortunately. I've been told to let them go because they won't kill the tree, but since it grows so slowly, I can't afford to let them live. They only seem to like the new growth and that's how it get taller. I've also had the flower buds freeze off in the winter, although not the last two winters.