Picked these up yesterday. After a conversation with my mate at F-One decided to go for the 14mm UHM over the 12mm UHM. He said in the F-One team the 14mm UHM is the mast of choice for most riders, providing that extra level of stiffness. The 12mm is mostly prefered by lighter weights, downwind specialists or straight line blasters. Basically its not "the 12mm is always better", its specialised tools for specialised uses, with the 14mm providing the most direct feedback and the 12mm providing the best glide.
Given my weight (100kgs/220lbs) and goal (freestyle / aerials & carving in waves in addition to the freefly blasting) I decided to bring home the 14UHM instead of the 12 in the end.
Will let you know how it feels compared to the old 14mm HM and 16mm mast, but putting it together at home and twisting the wings tells me this thing is ROCK solid. The difference is very clearly noticable in both bending and twist stiffness compared to the old 14HM with Titan 1 connection. I do feel a noticable chunk (say 50%?) especially of the bending stiffness gain is in the new Titan 2 connection. Therefore updating a 16mm Titan 1 to a 16mm Titan 2 will probably already be a major noticable improvement.