Your years spent undoing machinery like disabling traps yield you with new capabilities to quickly dismantle any technology. Knowing the very weaknesses of Eberron technologies your backstabattack now works on constructs.
I know there is whack construct, but that one is meh, this would be a worthy capstone to keep a rogue pure and be a good alternative choice/replacement to the much unloved "cheat death". If taking another capstone, make it, so the pure rogue is a little less squishy. I wan't to see more high level rogues running around, and not the current trend, "take a rogue lvl and the rest ranger", like most experienced people seem to do nowadays.