|Successors of||Iron Hands|
|Specialty||Rip and Tear|
|Allegiance||Imperium of Man|
|Colours||Red and Black|
Thanks to Forgeworld, Horus Heresy: Massacre has finally shed some light on these guys. Though it's not explicitly stated, anyone with half a brain cell can figure out that they were founded by Iron Father Autek Mor and his Morragul Clan (Mor's flagship was called the Red Talon for God's sakes). The Morragul Clan was noteworthy as being composed of some of the most bloodthirsty and hard-ass marines in the X Legion, so much so that even Ferrus Manus found them to be distasteful. Read: these guys were founded by the marines that even a Primarch known for beating a dragon senseless and drowning it in lava with his bare hands considered a bit too extreme.
To elaborate, Autek Mor was best known for killing several of his own men in duels over "slights" before the Heresy, to the point that Ferrus and the other Iron Fathers used his Clan as a dumping ground for those Legionaries who couldn't control their rage and fight with the self-control that the Iron Hands prized. After the Isstvan V Massacre, he waged a war that was pretty much the opposite of Shadrak Meduson's resistance. For example, he attacked Gethsamaine Colonus and blew up every major city. When the bombs went off, the population were hesitantly celebrating their liberation by the Iron Hands.
He also destroyed the World Eaters' main recruitment centre and muster world, Bodt, by dropping a fucking moon on top of it.
Outside of their founding, not a whole lot has been written about these chaps. What is known is that during the War of the False Primarch they, along with some other friendly fellows, wiped out eleven entire chapters that had been declared Traitors. Yeah... These guys don't play. Also went on a killing spree during the Moirae Schism when other Iron Hands didn't pick the right side of that little miniature Heresy.
Also of note is that, if the Codex artwork is to be believed, they are organized along Codex lines, rather than the Clan Council system of the other Iron Hands successors. Also of interest is that they are never mentioned as being particularly tech-obsessed. I suppose this should be taken as a given what with their heritage and all, but still it seems that Rip and Tear seems to be more of their thing than The Flesh is Weak.
tl/dr: Iron Hands successors that look and act like Flesh Tearers.