I just purchased a Zeagle Ranger, but I have having some doubts that I may want a BPW. What would be the main benefits of a BPW?
One additional benefit of a BP/W over a Ranger for the recreational, single cylinder diver is weight / buoyancy. The Ranger is rather positively buoyant which, for many divers, adds to their lead requirement. Particularly when diving in colder, salt water, where the exposure suit and water characteristics already mandate a considerable amount of added lead, using a 'floaty' BCD like the Ranger merely exacerbates that situation.
My original BCD was a Ranger. I still have it 15 years later. But, I moved to a BP/W years ago, for single cylinder recreational diving, and haven't come full circle, so the Ranger sits in my closet, mainly for historical reference, as much as anything. It is a well-made BCD, it fits me well. I simply prefer to add as little weight as possible. Plus, for me at least, the Ranger's integrated weight pockets put most of the added weight exactly where I
don't want it to be - 'below' my thorax (i.e. not aligned with my center of lift) and 'in front' of my vertical midline viewed from the side (coronal plane).
Would the choice between a BPW or Zeagle change if I plan to get a 40 cu ft pony tank?
Not really. My first pony bottle was a 40cf unit, I dove it with my Ranger with no problems. I dive it with my BP/W rigs with no problems. Now, I do find that i can streamline it a bit easier with my BP, simply because I can adjust the position of the chest and hip D-rings, which I cannot do with the Ranger.
The Ranger is a great BCD - rugged, comfortable, etc. I much prefer the buoyancy characteristics (and simplicity and modularity) of my (stainless steel) BP.