Sustain is the name of the game! Brittle-bronze, sometimes called by it's German name, "glocken-messing" (bell-bronze) is an extremely hard and very dense alloy. Because of it's composition, it is able to effectively store any energy that is transmitted to it, which is why--for centuries--it has been used as a material for the manufacture of bells.
A great deal of the energy that is generated by the striking or plucking of an acoustic guitar string is dissipated at the bridge and therefore wasted. The more solidly-built electric guitar utilizes its string energy much more effeciently than the lightly-constructed bridge area of even the finest acoustic guitar. However the new John Pearse King Pins eliminate much of that energy loss, acting almost like small energy 'batteries' at the bridge-end of each string, allowing a more efficient use of the string energy--and greatly improving both sustain and tone!
The number of pins you need depends very much upon the total characteristics of your guitar. A guitar with good tonal balance, string to string, would probably open up considerably by the replacement of all six original plastic or wooden pins with the new Pearse KingPins. Then again, just the replacement of the first, third and sixth might be sufficient. Just try and see!
If you have a guitar with a weak treble, you might just need to replace the first three pins--while one with a weak bass response should improve greately if you replace the pins that secure the wound strings. Incredibly, the replacement of JUST ONE PIN can markedly improve the character and tone of your guitar. Experiment! The tonal possibilities are endless!!