Anymore, I'm not so sure I buy the aluminum / oxide layer 'thing'.
I have a friend who uses an aluminum stock pot to brew with. I remember having a few of his brews about a year after I started brewing. I didn't know anything about ss vs aluminum but, I remember being taken aback when I found out he used an non-polished aluminum stock pot to brew in. His beers were great!
So, maybe there are other considerations that need to be taken by people who say they get a metallic taste in their beers. My friends aluminum stock pot is non polished aluminum. The surface of it almost seems rough. It has what appear to be microscopic groves all over it. He brews on a stove top, essentially heating the entire bottom of his brewpot all at once. A nice wide area of distribution of heat. It would be different if he were using a turkey fryer propane cooker. Using mine for example, he would get a LOT of concentrated heat directed via flame in a 7 or 8 inch ring in the center of the bottom of his pot. Being that his pot is non polished with those groves, I would think that he would run a greater chance of a metallic taste coming from his pot, literally. I'm not a metallurgist nor a chemist but, wouldn't the expansion of those microscopic groves raise the risk of leaching?
I feel like I am rambling a bit so, think of it this way. You can do this the next time you go camping... I remember being in boy scouts years ago and somebody showing us this. If you take a styrofoam cup filled with water, you can put it in the fire, just over the coals and that cup will take a very long time to melt, if it does at all. However, if you take a styrofoam cup filled with water and apply a flame from a pocket lighter to it, you'll melt right through it. This is what I am trying to convey...
That being said, I would think the people that are LEAST likely to experience this metallic taste would be those using built in heat elements, where there is no 'direct' heat being applied to any surface of the pot. Instead the pot is heated by the water that is inside of it.
Now, I'm curious... lol I'll have to give him a call and see if he'll let me borrow his pot for a weekend. I use an ss pot personally. It would be fun to throw an expensive smash recipe together and see if I can pull off a metallic taste with his pot...