I think I understand you perfectly. I would not choose Beast Slayer, it only gives a bonus some of the time - when Fighting Beasts. If you're planning to make a TWF character, why on earth would you not get the TWF talent ?
The Talent system appears to be suffering from the same issues as D&D Feats - stuff that's useful all the time, and stuff that's only useful in certain situations. Most of the added actives seem pretty garbage to me as well, I'd never pick them over stuff that gives me a flat passive bonus all the time.