The B17 is the oldest saddle design that Brooks England still manufactures (since 1888). This Special model comes with copper plated chromoly steel rails and hammered copper rivets. It makes a nice replacement or upgrade over the stock Brompton black saddle. Leather saddles are more organic and slowly break in over time, eventually (if well-cared for) achieving a "custom fit." The thick leather is also generally more durable than the more common stitched material saddles out there (synthetic or otherwise). Lastly, since you'll generally be bringing the Brompton in with you everywhere you go, there's no worry about leaving a tempting Brooks saddle where a would-be thief could spot it or where a rainstorm could soak it. And who doesn't want their English bike to have an English saddle, too?
Brooks designates shorter saddles with an "S" after the model number. The B17S is 235mm or 9.25" long. The standard size Brooks B17 is 280mm or 11" long. Why might you want an "S" over a standard length? Brooks designed the "S" originally to be for women. Apparently the rationale behind the shorter length isn't any difference in comfort, but that it gives a rider more space to step into/onto a bike with a step through frame. Obviously anyone of any gender can ride a step through bike, so we'll just let you judge whether you want the shorter saddle.
If you're buying this saddle to go on a Brompton folding bike you're also purchasing through our store, there's a checkbox you can toggle on the page of the Brompton bike you intend to buy. Checking it lets us know you want the Brooks upgrade and refunds you the cost of the standard Brompton saddle, making the B17 total cost $105.