Bottom magnets refer to the magnet location closest to the actual button and Top magnets are a reference to the magnets furthest from your button
A "bottom" magnet is actually comprised of 2 magnets for further versatility in setting your buttons strength/stiffness.
Clones have a slightly smaller diameter in which to place magnets and these will not fit in them
Neodymium magnets are brittle and fragile. Neodymium magnets are made of a hard, brittle material. Despite being made of metal, and the shiny, metallic appearance of their nickel plating, they are not as durable as steel. Neodymium magnets can peel, chip, crack or shatter if allowed to slam together. Eye protection should be worn when handling magnets since shattering magnets can launch small pieces at great speeds.