I don't think JL branched off, but rather aquired TMA as a subsidiary. It gave JL dealers a relatively inexpensive alternative to offer customers who would have normally bought a competing brand. Meanwhile JL still pulls in the profits that would have normally went to some other company at that price point. IOW, it's JL's way to attract customers who wouldn't be buying JL Audio's namesake products.
As far as experience, I've used their 6.5 components, 6.5 and 5x7 coaxials and some of the first gen. amps. The amps aren't bad, they were solid IME and just what you'd expect from a budget line. The speakers were what really surprised me. The components I actually preferred over the lower end JL's. They were much smoother and more defined. The coaxials were also solid performers and better than many more expensive offerings I'd auditioned.