I did drysuit, ITT, then AN/DP from a local TDI shop/instructors. My biggest challenge was/is getting more time in the drysuit and doubles combination. As far as I can tell from following Marie's posts, she has a lot more time in the configuration than I did, and I think that's a good predictor of success. FWIW, the biggest lesson I learned after the AN/DP checkout dives was the difference in my own experience / awareness / tolerance for being narc'd at ~140' with a very moderate 'under-instruction' tech task loading compared to my recent rec dives in the vicinity ~130' with nothing specific to do but look around and take photos. My own specific clinical sign is absence of any symptoms of which I am aware, or absence of any memory of symptoms of which I am aware, but clear reviewable evidence after the dive of spending way too long looking at and trying to "fix" a fouled reel before finally giving up on it (and putting up with a lot more deco than the plan!)