I have not had any trouble with my Ranger and I can't see any way that it can happen (losing weight)with the Ranger. My wife dives a Diva with slip in pockets that are held in place with velcor, she has had no problems. There was a thread a couple of days go that ask the same question and as I recall, no one had had a problem. Try a search for it. Now these are both high quality BC's, the lower cost one may not do as well (a guess, not backed up by info). On the other hand, I have seen and have had happen to me, weight belts spinning around and/or getting loose esp when you are wearing a wetsuit. As for carring the BC's, both ours have removeable weight pockets. You simply remove the pockets just like you would remove a belt, you just have 2 smaller thing to hold on to.
There are actually 3 types of BC's:
The vest type- These have an air bladder that wraps around you with some of the bladder actually in frount of your waist. Most likely the type you rented/trained in. These tend to squeeze you when it is fully inflated. Some people don't like this but they tend to float you in an upright position at the surface.
The back inflation type- My Ranger is one of these. All of the air bladder is located behind you and around the tank. These don't squeeze you when fully inflated and usally offer more lift than the vest type. Some have interchangeable bladders. They do tend to float you face forward at the surface but this is fairly easy to overcome with a little experience.
Finally, there is the Backplate/wings combo. These consist of a metal backplate with a simple strap arrangement to wear it with. Attached to this assembly is an a air bladder that can be easily changed with other sizes. These are more "customizeable" than the other types of BC's.
Which is best, well that's one of the hottest debated question on the board. Each group has a bunch of reasons why they think their style is best. Some of the reasons I buy and some I think are BS. It really depends on the type of diving you are doing, what your budget is and most important, which type YOU like the best.