I have more difficult imagining the Raven guard using a fell blade than the 'scars. I can imagine the scars using it like a mobile command center for their mobile forces, like a mini chapel fortress- possibly drawing inspirationg from genghis kahns giant yurt
On the other hand its harder to imagines striking from the shadows with a tank the size of a city block.
I'm also having difficulty imagining the ultra marines one, because fluff wise they are the marine default standard or vanilla flavour and the fell blades are all unique. I suppose it would have loads of greco-roman imagery but apart from that can't think what weaponry etc