I'm pretty late to reply it, but it doesn't work agaist AG monsters because they don't negate any traps, they only prevent trap (and spell) cards to be activated. Preventing and negating are 2 different things, it's the most basic rule in ygo, if the names are different, so they aren't the same thing.
Rushed for the last 4 hours from 800ish notebook points to 120ish. Got 2 prismatics for Ancient Gear Fist and Ancient Gear Knight. Thanks Kefka v.2.