When purchasing a BCD ensure it has a hard backpack. Soft backpack BCD's were designed so they could easily be rolled and packed in a suitcase; they were not designed to dive
with. As you can see from these photos they do not hold the tank in place and certainly do not work if a pony bottle is used. Divers who wear soft pack BCD's have a very difficult time performing the over-the-shoulder regulator retreival procedure because the moment they lean back even the smallest bit,
the top of the tank leans back out of reach. To retrieve their regulators, these diver have to use their left hands to push the bottom of their tank upwards and away from them, which will bring the top of the tank up and towards the back of their necks. The over-the-shoulder regulator retreival is the best method found for retriveing a regulator.
To have good buoyancy control, to be able to swim and work over silty bottoms and not kick up any silt, to be able to rotate and work inside vehicles, etc..., you and your gear need to be one. When you move, your gear needs to move with you. If you move and then your gear moves later or in a different direction, then your gear will change your position in the water without you wanting it to. This is one of the many reasons that all gauges and pony regulator second stages need to be secured against you, preferably in the golden triangle area (A triangle from shoulder to shoulder with the bottom point at the navel - designated by Dr. Glen Egstrom). If you rotate slightly to your right while horizontal, a soft pack BCD will allow the tank to drop to the right, rotating you further than you wanted. However you move, that soft packed tank will pull you around. If you are wearing a soft pack and have not noticed this then you are not working with perfectly neutral, fine adjustment buoyancy control technicques - which is what we find more often that not. Not many instructors have great buyoancy control, let alone know how to teach it. The evidence shows that most divers are overweighted by at least 6 lbs.