First things first.
1. It's Tartaros.
2. Terminators can't Deep Strike without a ROW, special character or legion rule which allows them otherwise.
SInce you @lord krungharr plays IW just like me, we talk Perturabo, who allows that or the couple of RoW which do the same.
3. WE Terminators can't take Chainaxes. The Cataphractii poweraxe looks like a Chainaxe, though.
I've got 2 units of Cataphractiis already (plus 10 Tyrant Siege Terminators). Was wondreing if I should mix it up for my next terminator installment and get some Tartarus ones? They can run if needed, and Sweeping Advance. That seems pretty good actually as if I'm not mistaken Astartes can be swept in combat in 30K can't they? (haven't actually played yet but will soon).
Plus they kinda look neat, very sleek. Not sure if I'd give them all lightning claws, but maybe just power weapons, a fist or two, and some combi-meltas. I'd probably magnetize them too, the plastics are easy to do.
Or does the 4++ trump the Sweep?
Tartaros are great in Zine Mortalis games.
I use them like expansive tactical squads there, because they can run, which gives them an advantage over Cataphractii, they don't suffer of the "void" special rule in ZM and they can take Chain- and Powerfists to fight dreadnoughts and doors, which are a common sight in ZM.
Since you start with your army split in two in ZM I let Tartaros start and deep strike with Cataphractii later on what the can because I always play the zone Mortalis Assault RoW. That works very well.
In open battles they are obviously a little less appealing because they don't field a 4++, but they can run, which allows them to footslogg while Cataphractii has to be transported to get anywhere.