Telling Blow

[calighis]

So what if I am already doing sneak attack damage on the crit? I guess it would be too much to hope for that I get a double stack of sneak attack?

 

[jaelis]

No, TB just gives you one more way to score sneak attack. Just like if you flanked a surprised foe, you would get sneak attack only once.

 

[NightCrawler]

Lets say you crit while you can sneak attack anyway. Only the one sneak attack is enabled and not the extra sneak attack given from telling blow. In other words Telling blow lets you make a sneak attack only when you score a crit hit and YOU DONT GET a sneak attack.

 

[moritheil]

Telling Blow, as others have pointed out, gives you an additional condition under which you can add sneak attack. If you are already adding it, there's no point.