This is the reason prisoners are so healthy and full of vim and vitality. (right........)
UMMM I don't think you can get iron in your diet this way. First off, it's unlikely you're going to find a bar of pure iron anyway, since most metal bars are composites of many minerals.
Also, the iron has to specifically be in an ingestible form so the liver can process it. An iron bar ain't a lollipop. (maybe that should be a slogan for something).
When they say that cereal has added iron, they really mean that actual bits of iron are added (very tiny particles). You can use a magnet to pull some of them out, they're little iron filings.
So if you file the bar down first and eat the filings, MAYBE it would contribute to your iron intake. But - why not just grab some milk and eat the cereal instead?