I must admit that I like the sound of these guys when I first read Extermination. In brief, they are standard cataphractii terminators that are each armed with a cyclone missile launcher, a power fist and combi-bolter. On top of this, the squad sergeant carries a special device that permits the individual with split fire and night vision. This can be such a huge boon!
But it gets better than that: each and every attack is a wrecker one, regardless of the source (melee, weapons, whatever - its all a wrecker attack!).
The main drawback however is the price tag. They cost 150% of a baseline terminator squad. But for that, we are gaining a lot more, I would think. The sheer attraction of the cyclone missile launchers simply cannot be overlooked. From turn 1, they should be pumping out much needed firepower support whilst slogging up toward enemy positions. But they still have only one wound each. So perhaps augment the unit with the addition of legion Primus Medicae in terminator armour to help out. This starts to get really expensive though, so beware.
Here are a few example builds.
5 Tyrant Siege Terminators (295 points).
The naked version will serve very nicely in my opinion. Add in a character to taste. And or a land raider!
8 Tyrant Siege Terminators, 4 combi-plasmas, 2 chainfists (475 points).
This is a flexible squad for taking out light tanks, enemy 2+ save models, as well as being a close combat danger to terrain and vehicles alike. And the price tag seems to be relatively okay overall as well. Arguably.