Hmm... On the one hand, joining this third faction might not end well. Hero Factory and the Throwbots may not appreciate having BIONICLE--the ones they replace and the ones who replaced them, respectively--try to join their ranks. On the other hand, they let Matoro Inika live, and with a roughly even split, the Tahus aren't likely to make much progress defeating each other. This third faction (choice one) is probably the wisest.