I love it! More yuri goodness absent from the anime. Wish there was more of Momo licking though.
My bet is on Momo or Hanzo being the traitor. If it's Hanzo she's probably doing it because she seems like the type who would "betray" her friends in order to gain the trust of the enemy organization to order to defeat them. Also, sets up an interesting confrontation between her and Momo later on. Kind of an obvious choice, but I'll stick with it.
Momo being the traitor would be the "big twist" as expected from the author of Yuuki Yuuna. The anime is already kinda dark with rampant drug abuse and forced prostitution rings, so Momo pulling a fast one on the viewers isn't out of the question. Would also explain her ridiculous eye-sight and tasting ability that seem unusual for someone who initially had zero spy experience.