I don't understand how the point is moot when all the text - in the RPG and in the novels - backs that you need a metallurgist in order to get a specific alloy of metal, and that burning impure metals is relatively dangerous.
I said the discussion
is moot, not the point. People were discussion the likelihood of finding Allomantic metal in every-day items under different circumstances. I don't think this is worthwhile and GMs should, in doubt, just roll a die to decide. This general rule allows you to bend it for special situations but nicely prevents Allomancer character (or rather the players) to get away with cheap metal if the risk is not countered by exceptional need.
EDIT: Also, does that Stunt come with a drawback? For instance, only receiving passive benefits(pewter endurance/healing, iron/steel's blue lines, etc.)?
No drawback for this one. You take it and it works.
Wait; doubling the burn rate would mean burning it away in half the time it usually takes. Does the stunt do this or does it double burn duration