I have had 1 game so far, against Death Guard. I almost tabled them (Warlord on 1 wound). Melta Seraphim are amazing, Repressor is great, Heavy Bolter Retributors did next to nothing. Oh and Storm Bolters are really good. I think Retributors will have to be put in a Repressor with 4 Heavy Flamers or Multi-Melta to be useful honestly(Or something similar). Basic Heavy Bolters aren't enough.