I agree that I have a hard time fitting him in due to an overcrowded hero slot.
Yeah, I love the model and try to take whenever I've got a spare 55 points in my hero slot. Which so far has been in two games. BSB, captain on pegasus, warrior priests for every combat unit will more than chew up the hero allowance by itself.
In one game he did basically nothing as I deployed him poorly and then got cut down before he even got to attack. In the other game he did little, but forced the enemy to change his whole plan to avoid getting Killing Blowed, which proved a pretty significant factor in my win (though that opponent is unlikely to make the same mistake again, nor would an experienced opponent).
I mean, he's hardly a powerhouse that will regularly swing games my way, but nothing should be for 55 points. He's a lottery ticket, throw away some disposable points, have some fun with him and just sometimes you hit the jackpot. And sometimes it might force a very risk adverse opponent into making a mistake.