to above post. Personally, I really do not believe that pally tanking shines until 70 level content. To be honest, spell damage plate gear doesn't even start dropping till u hit outlands.
When i rolled a pally tank, I rolled it cuz i thought it would be cool to 1 pull the ship in deadmines or the SM armory or stockades etc. honestly, any 70 could do that probably. It takes much more focus to become an effective tank tho.
Gearing/speccing for that and for regular tanking in higher level content is much different. at lower levels, righteous fury and salv on dps is more than enough to help u hold aggro. i think blessing of sanctuary is actually a better choice for those lower level instances as well. Until 10% more life becomes a necessity.
to answer your question since i have strayed, i dont think B of crusader is worth it. if you are leveling in prot spec, might as well stick to that talent tree or get up to Seal of Command in ret tree just in case u decide its faster to kill mobs with a 2hander imo.
Although, every level has an area where u can easily farm multiple melee mobs ^^