This will probably be the final segment on the continuing discussion on selecting of BCD's for the beginning diver.
Cummberbund / Cumberbund: Most current BCD's on the market have a sash like waistband that generally goes around the stomach of the diver and has velcro fasteners to secure it in place. The purpose of the cummerbund/cumberund is to keep the BCD in place and to prevent lateral movement.
It is important to remember that as you descent in the water, the water pressure will cause your wetsuit material to compress and you might find that the cumberbund might be not as tight at depth as at the surface. Do not overtighten the cumberbund fit when donning your gear. The cumberbund should fit snug around your stomach, but should not be so tight that you have trouble breathing or moving.
There are some designs that rely on buckles instead of velcro fasteners. I have both system on various BCD's that I own. I don't have a strong preference for either system, but if I had to make a choice, then I guess the buckle system feels a little more secure to me. However for the beginning diver, a velcro system works very well and it easy to use.
Releases: There are various styles of releases on BCD's. The primary purpose of the releases is to enable the diver to doff (take off) the equipment quickly and safely. Releases will be found on stomach belt, sternum belts and on the shoulder harnesses. The purpose of the various belts is to keep the BCD securely fitted to the diver. When choosing a BCD, try to select one that has a sternum belt as well (some don't).
There are differences in the way the releases operate (between the different manufacturers). Select a style that you find easy to operate. If you will be using gloves with the type of diving that you do, use the gloves in the store to see if you can operate the releases with gloves on.
Safety tip: always make sure you know where the releases are on your buddy's gear and that you know how they operate. You might have to assist your buddy in the case of an emergency and it is vital to know how to quickly locate and use the releases on his/her gear.