The fluff for them is rather like the Cephalyx and Drudges from Privateer. Granted, I'm not sure exactly which one came first, as my 40k lore hasn't really been updated since just before 4th edition.
The two sets are available to order and will be shipping out right away.
From the release:
Relentless and indefatigable in battle, Tech-thralls will advance into the most ferocious enemy onslaught without fear, an army of the alive-yet-dead puppeted by the magos who command them. Theirs is a fate suffered by those who have failed their Mechanicum overlords in some way, their consciousness and memory overridden and their bodies converted through basic augmetics and cranial surgery, so that they are still considered human, but are no longer capable of independent thought or action.
On the battlefield, Tech-thralls are formed into Covenants, utilising numerical superiority and weight of firepower. Their dull response to injury, capacity for adaptation and relative ease of replacement seeing them used as expendable foot soldiers for the armies of the Machine God.
Mechanicum Tech-thralls with Laslocks and Tech-thralls with Mitralocks are now available in sets of 10 for £35.00 each. These are multi-part resin kits available to order for immediate dispatch.