I have the Iron Hands set, and the Deathwatch set - the only similarity is that when painted they are both black with silver details, and that they are both based on the normal plastic marines.
The Deathwatch are simply standard marine models with enhanced bolters,
DW shoulder pads, and helmeted heads with targeters. The Iron Hands set is a plastic tac marine set with two metal legs pieces with bionics, thunder hammer, 2 arms with bionics and 2 bolters with extra bits on, 2 torso pieces, 4 metal heads with bionics, and 10 shoulder pads.
Deathwatch:
Iron Hands parts: