Nicholas,
As I recall, they work the same as the ones on a Violin or Cello. You would tune the instrument with it's gears on the headstock, and then use the fine tuners for adjusting the pitch in smaller increments. I think that they are perhaps more useful on instruments that use pegs rather than gears, or an older instrument that has gears that are worn, like mine. I'm fairly certain that you could just buy the fine tuners and put them on any bridge, but I haven't looked for them in a long time. The metal tailpiece isn't something that I'd be excited about. Mike Pecanic makes these wonderful compensated tailpieces. I have one on my bass It improved the lower notes, and it's a lot prettier than the basic black ones. He makes an adjustable one as well, but the adjusters aren't fine tuners.
http://www.mikepecanic.net/products.html
Ric
