Mechanical Cartridge Vambraces - how do these work?

[Orthin]

Before I buy some I am curious how exactly they work. I have read through the Wiki snippets and still do not fully understand them.

For the cartridges, if I want to TWC, do I need 2 cartridges or 1? Do I need weapons of the cartridge type to put in them or is the item in the cartridge and is 0x? How do I get these worked on, do I give the cartridge to someone and they enchant, ensorcell etc...They look very neat but I am genuinely confused and don't want to spend anything without having some idea.

[Ashlander]

All I remember is that you give the cartridge to do the enchant/ensorc, etc. It currently can use sai, dagger, main gauche, short sword, katar and handbow weapon types. You can insert one of those weapons into it but you can't remove it once done.