It may actually be easier to carry-on the BP. I recently travelled Ottawa - Washington - Los Angeles - Sydney - Cairns and had to pass through security at each leg (long story). At each airport (except in Australia), my checked luggage was opened because the backplate clouded the x-ray of my dive light (no batteries) and my highly suspicious wet suit. In Washington I was called back to explain why I had a metal plate and a "book" in my luggage. I guess dive logs are dangerous cargo now too :06: . On the way home, they even lost my new TSA approved lock.
I decided to carry my HID becuase I thought the battery canister would look suspicious on x-ray. Ottawa was the only place were I even had to pull it out, and luckily one of the security guys was a diver and recognized it right away. In Washington they had to call over a supervisor to make a call on those dangerous looking regulators:11: . HID canister, no problem.