Boomeranger Final Blow

You know, I'm kind of ashamed to have to ask because I'm a Boomer main, but there is something I need clarification on.

So lately I've had to do some thinking about Attack Speed and which classes need it and which classes don't. Being a Boomeranger main myself, Boomeranger is always at the top of my list, followed by Neon Ninja and debatabley Pirate Captain and Revenant. However, there has been something in the back of my mind about that. From my understanding, the reason you run Attack Speed on Boomer is so you can get the third attack for Final Blow quicker. However, I'm using a Sword Boomer, and I know that Sword Boomer does a Spin Attack for his third blow. The description of Final Blow on the character page is "Every third attack does extra damage." However what worries me, and what I'm wanting to ask is this: For sword Boomer, does the "extra damage" refer to the fact it hits everything around him or does the attack just do extra damage on top of hittng everything around him. I asked around a bit today and I've gotten mixed answers. So guys, whats the verdict? Did I botch up my stats by giving everything Attack Speed or am I fine?