Normally when you open a compound device (a device with multiple components), you have two options. You can either open only the highest capacity piece (say a gem), or you can open the entire thing, provided you have such a high magic theory score (or Verditius Elder Runes, but that's another issue entirely) that it's possible.
When you invest effects in the item, you get the shape bonuses for all the components, but you only get bonuses for the materials you opened. A wooden staff with a gem on the end doesn't get the bonus for the wood, just the gem and the staff shape, if you only opened the gem. At least, that's the example given in the book.
Since Lesser Enchanted Devices, Charged Items, etc. don't need to be opened, this doesn't seem to apply to them. It looks like you could use any shape and material bonus applicable to the effect.
Now, Talismans... here's where I'm a bit lost. The example in The Mysteries, on page... 89? I think. Around there. Has someone opening a talisman as a compound device by just opening the highest capacity part, and then still having access to ALL the shape and material bonuses of the item. Is that right?
In my saga, I've ruled that attuning a talisman spreads the enchantment out so that it does work like that even if it was opened with the lesser of the two compound device methods, because I think talismans with lots of components is very thematic. But I'm curious if anyone has an actual interpretation of the rules to apply here.
Not -quite- true.. the example you quoted is -semi- right.. but.. not right for what you're saying exactly.
That example is not an example of a compound item.. it's an example of an enchanted gem stuck on the end of a staff. You are literally just enchanting the gem, which happens to be on a staff.
Whereas, with a compound item, technically you're enchanting the whole item, even if you don't actually open every bit of it.. that's why compound items get to use every shape and material bonus available.
Downside being, that you have to open the biggest and most important piece of the item.
In the example of the staff, let's say you used wood, which has a 24=8 cost to open, and the gem (priceless ruby) needs 201=20 vis. If you were making a compound item, you'd have to open the ruby, it's the focal point of the entire item. If you were just enchanting it normally, you could enchant the wood if you preferred, thus letting you use less vis. Downside is that you don't get the material bonuses of the gem (which in this example makes it rather pointless, yes)
Consider however if you had a staff made of ruby and a diamond on top, then you could get the staff bonus and not have to pay a scary 80 vis. And you'd have a swanky staff ^^
Also worth noting is that if any part of the item you actually enchanted (as part of a compond item) is broken, or removed in some way, than the item is broken and no part of it works.
If an item you've only enchanted part of (say the gem on that staff) is broken, you only lose those effects that depended on the bonuses given by the part(s) lost...
Also, for the non-compond item, you can enchant each part on its own - getting a magical staff with a magical gem attached....