I saw Double Slice discussed in Alpha 1 forums but I think the feat needs more clarification.
Double Slice reads:
"When wielding two weapons, your off-hand weapon can be used with great effectiveness.
Prerequisite: Dex 15, Two-Weapon Fighting
Benefit: You gain +2 circumstance bonus on attack rolls made with one light weapon while attacking with two weapons."
Which one is it, off-hand or light weapon? At the moment, I'd say the rules restrict the weapon to light, even if used in your main-hand. Is that the intent? Or to restrict your off-hand weapon, getting the bonus, to light? Clearly, an off-hand weapon that is not light can't get the bonus.
To make things more complicated, how does that work with TWF monks? The FAQ states about two-weapon flurry: "She can use an unarmed strike as an off-hand weapon." The FAQ uses clarifying examples where unarmed two-weapon flurry is allowed. Does this mean that monk's unarmed strikes are considered weapons for Double Slice? That is, can a monk use Double Slice bare-handed?
Two-Weapon Defense spesifically excludes unarmed strikes, while Double Slice doesn't.
Found the Alpha 1 version of the feat. From that it's pretty clear that A3 Double Slice is usable with primary hand, as well.
"Benefit: you gain a +2 circumstance bonus on attack rolls made with your off-hand weapon."