What's the standard interpretation? I'd like to be able to use this guy with multiple GMs.
You'll be, don't worry.
My interpretation is that with this maneuver you use one of your two wepaons to defend yourself, which allows you to get full defense without spending any action, but it only works against melee attacks ; against ranged attacks, you make your defense test with only reaction, as usual. It's powerfull, since it means you're in permanent full defense for free in melee, but not overpowered, and it doesn't make the classic full defense useless, since it's the only option working against both melee and ranged attacks.
Bradd's interpretation is that this maneuver allows you to get the free full defense both against ranged and melee attacks, which is broken to my point of view.
I don't know the main interpretation. Mine seems more logic to me, but maybe I'm an exception and I just don't see it.
So, whatever your GM interpretation is, this maneuver is still very powerfull. It's just a little bit "overpowered" in one of the two interpretations.
EDIT : I don't know if riposte and so can apply if you use your guns for shooting your opponents. They sure apply if you use them like clubs, but then it's not really interesting for you since you're not very strong. Would I be your GM, I wouldn't allow "riposte" or "finishing move" to be applied to shots, or, for exmaple, it would allow a character to make a simple action shot, then a second shot, and then finishing move, a third shot.
Take care with these maneuvers, your character is based on a very vague style, that can be interpreted in many ways. If you play this character with many GM, some may apply or not these maneuvers to guns.