Does the bean bag style weight system put much strain on your lower back?
It is a little better than a lead block and webbing belt, the main benefit is no hard corners digging in to hips. They are also less unpleasant to drop on your feet or trip over, they still hurt, but they are less likely to remove toes. I'm not sure if they'd make that much difference to your back, but I can only see them as being an improvement. The only problem is, when you go on holiday, you tend to have to fill the pockets with the solid weights, as the boats don't generally carry the beanbags.
I initially chose to spread my weights between two systems so I could go out with a freediving friend without having to keep re-weighting for scuba, I found myself frequently in this unconventional buddy pair (Freediver / Scuba Diver) and generally find this grouping gives me the benefit that someone knows I am there, and the freedom to take photographs at my leisure, (photographers don't make good buddies).
I'm not advocating anyone else do this, as there are safety issues that need to be managed, however I have fully redundant gear, and chose my weight distribution to complement that style of diving, My theory being that I need to be able to recover myself from any situation that occurs. So I think about what could happen. Most of the issues I could foresee related to air, weights and entanglement. When people think about emergencies, frequently we tend to think about how we would behave in one, but I'd recommend anyone to sit and think carefully through how your kit will behave, because it's very easy to think what you would do, but generally some of your decisions are likely to be made for you by the equipment you wear.
The best way I could see to counter most hazardous situations, was to gear myself so that I can transform quickly, from a Scuba Diver, to a freediver with a pony bottle.