When flying over water, I wear a vest and carry a fully charged HEEDS III. I looked at the SCBA and other types, and didn't like them. You may have a little more air, but the extension tube is cumbersome and it could get caught is something. The HEEDS III is always ready, no switch or valve to turn on... just put it in your mouth and inhale. It is small, portable, and you don't have to hold anything once you place the unit in your mouth. I recommend putting a rubber quick-release tab on the carrying strap to make it easier for removal.
Also, I recommend that you spend the extra money on a HEEDS III system WITH a pressure indicator valve. The standard unit has a simple "push & release" system to see if it is charged, but that doesn't tell you how much air is actually in there. Anything less than the top of the green is unacceptable. I've tested mine and I get about 22 FULL PANIC breathes out of it (at least that's what I count when exaggerating my breathing).
Finally, your safety equipment will need a maintenance schedule. Grommets and rubber valves should be replaced annually. In addition, you should apply silicone lubriciant to your o-rings and other areas about once a month (I do it each time I fly over water, but that isn't often for me).