I am already running a sentinel squadron as a flanking assault support unit, and I would rather they be at the sharp end than hugging my own baseline.
I finally managed to win a game today with my Guard and having a penal legion squad right on the flank was extremely useful. They managed to take down a random lone spawn and then follow up into a flanking Chosen unit. They got torn to shreds, along with a Veteran squad, but they held up the chosen for long enough for my Hydras to turn and address. Hence the speedbump approach appears to work.
I think I will continue to try this tactic until it shows obvious horrible flaws. Any other opinions or thoughts would be welcome though.
Unit of honour was definately my Vendetta though. Stormed in on Turn 3 to smoke 2 Obliterators that were threating my whole vehicle line