It's a lower power cpu than the nTB Pro, though a more recent model (I've not dug out the part numbers to properly compare specs). Otherwise while there may be fine details different, there's not a lot between it and the nTB Pro based on the headline specs. And it even offers the touch id sensor, which the nTB Pro does not.
So it really isn't obvious to me who the nTB Pro is supposed to be for now: it offers limited benefits over the new Air and has at least one drawback (no Touch ID) for slightly more money, whereas it's significantly worse than the TB Pro. Personally I'd phase the nTB Pro out at this point, but who knows, perhaps there are still enough people who buy the things for Apple to sell them even if they don't really make any sense?