First off, he is considered to be the Crowe tax, because he is how you get your Purifier squads to become troop choices. Generally people consider him horrible on the tabletop, myself was included until this last weekend.
Before, my tactic with him was to hide in the backfield, hop into an empty rhino, and look for a independant character or monstrous to take down with Heroic sacrifice. During the tournament however I started using a different tactic and it worked rather well.
I started him off pretty much the same. In the back, jumping into an empty rhino. (those purifiers like to get out for full on heavy shooting). He then moves up, looking for his opportunity to assault a unit. When he does, instead of attacking with one of the other stances, use Blade Shield. This allows you to re-roll failed saving throws until the end of the phase. That means you are re-rolling either a 2+ armour save, or a 4+ invul save when failed. He has a weapon skill of 8, so is hard to hit and has two wounds.
With blade shield, there is an excellent chance for him to survive his opponents. However, the first thing I do after assault moves is use cleansing flame. This allows for me to roll to wound every model on a 4+. So I charge in with Crowe, have a chance to wound a small unit, and a good chance for surviving.
I know its pretty simple, but I am sure there are lots of players out there, just hiding him like I was, looking for a Heroic Sacrifice move.
Even though Castellan Crowe is still not the strongest out there, I think the Blade Shield + Cleansing Flame combo makes him much more usable on the tabletop. Taking this approach gets the most out of having to pay the Crowe tax, and if the opportunity does arrive to use Heroic Sacrifice, its still there.