DATS is very useful. You can check capacitors, resistors, and inductors. It's a signal generator, and you can use it as an o-scope. Like dbjunior said, it's great for checking resonance and impedance curves with the sub in an enclosure and in the vehicle. You can use it to get the impedance curves of your mids and tweeters and use that data to design a good passive crossover.
It's good for someone who uses all these extra features, but it's not worth buying if all you do is build beast subs. TSP's are not very important for beast subs anyways but can be pretty important for lower power or SQ stuff.