There is a plate that attaches to your tank, wing, and harness. The plate is often negatively buoyant, by a tiny bit 1lb. or a fair bit 5lb. It sits behind your buoyant lungs.
Everybody's body is different. But lungs are particularly buoyant; like a really buoyant ballon attached to an elementary school playground see-saw near the 'head end'. The BP/W plate sits behind your lungs balancing out the lungs effect on trim, making it easy for the see-saw to stay level or at any other desired orientation.
Where you put negative things affects your trim, just like where people sit on the see-saw affects the trim of the see-saw. Everyone has a different best lead distribution. To get to neutral trim, you can put lead at various parts of the harness, as it is made of 2" webbing throughout, or at various points on the plate, such as with zip ties through holes or with gorilla tape.
A BC that puts ballast by the lungs is a no-user-action-required start at getting in neutral trim. A BC that gives wide flexibility in distributing additional lead gives a great start dialing in neutral trim further. And is generally more helpful for trim than a BC with plastic behind the lungs and emphasizing big pockets down by your waist/hips for lots of lead with some afterthought trim pockets part way up the back.
It's just an elementary school playground depth of understanding. If we want to attach some harness to the see-saw, would we go with a steel frame under the ballon, or a plastic and buoyant padding frame under the ballon and pockets for some lead further away from that end of the see-saw, possibly even on the opposite half of the see-saw.
but apart from remembering to thread the crotch strap ...,
what is difficult about a PB/W?
BP/Ws come with options. Elementary school bicycles come with options. They also come as size X generic packages. There are tons of things you can do to a bike given a performance or appearance tuning catalog and shop.
But you do not have to. You can get a plate, harness, wing and enough pockets for the lead you expect to need
as a package. It will start you out with a fair bit of ballast in a spot that does a lot of good. If it seems not quite right, you have lots of options of where to put lead close to your body, not sticking up behind you on your tank. Care for more/less of a wing, you can change just that. More/fewer pockets, you can change just that. Want some color, get colored webbing, wing, or plate.
