I like mangled metals!
Well, I like it better when things work, but I like getting a half a second chance when they don't. Mangled metals add fun, they add complexity to the crafting process.
We could imagine a rationale that in making jewelry, since we obviously need to reduce our ingot to little tiny bits of metal to make a ring or links of a chain or whatever, there is no chance to recover anything resembling an ingot and thus no mangled return. (Although I think in RL jewelers do know how to recycle even little bits of material.) Not that I wouldn't be happy to get mangled metal back from jewelry failures too. But I can understand it.
But at least it seems like tinkering ought to be consistent in always (or never, or at some consistent probability level between always and never) returning mangled metal - no reason that arrowheads are different than gears.
And musical instrument crafting too...we use metal and should get mangled metal back on failures. I haven't made that many harps and I don't remember right now, but I don't think we get anything currently.
IMO the fact that conversion of mangled metal to a fresh ingot has a chance of failure (and a very good chance of failure if the character doesn't normally do smelting and so has a low skill level) is the right place to balance the efficiency. Needing two mangled to get one ingot back doesn't necessarily make sense to me, and certainly would be a nuisance for those who only get their hands on small amounts of metals at a time and aren't doing mass production. And there's an easier way to fix the weight discrepancy:-)
If we think the system is unbalanced maybe the chances of success for converting a mangled metal back to an ingot should be lowered even for people with higher levels in smelting, to keep it so the process is not perfectly efficient.
