Mostly you'll get a bit more iron in your diet. I'd take that over tiny flakes of PTFE anti-stick coating. Or you can soak the loaf pans in a solution of oxalic acid (a good quantity of Bar Keeper's Friend mixed in water) which will convert the ferrous oxide into (some other iron compound) that is physically less friable, and blackish in color.

Almost all my baking pans get rusty if I am not careful about drying and oiling them after I wash them. I just try to wipe the rustiness off with some grease and a paper towel, and it usually is fine. There is maybe a slight metallic taste to the finished product, but only if you are thinking about it.

I have rusty baking pans. Sometimes if I think about it I line them with foil or parchment paper. Either works for the majority of items.

I would scrub off most of the rust*, dry the pans well (in a warm oven), and not worry about it unless you're seeing flecks of rust in the food.

Here's what I do when I'm baking in the rusty bread pans at Mom's: I scrub out the rust, especially in the edges and corners. I dry the pans. I rub them clean with a towel. While the bread dough rises, I butter (or oil) the pans. If more than a tiny smear of rust rubs itself onto the buttering [brush/rag/paper towel], I know I didn't get them quiiiite clean enough and I wipe the pan down 'til it's clean and re-butter.

* Triode's rec of Barkeeper's Friend is a good one. I just bought a canister and was AMAZED at how well it cleaned my mottled, rusty old baking sheets --- better than steel wool, even. Just scrubbing with BKF and a sponge got off spots and stains and rust-accumulating rough patches I had long assumed were permanent.

When I use my old bread pans, I have to remove the bread promptly, or it imparts an off flavor. A good cleaning, followed by oiling the pan, then baking it, as with cast iron, might seal it a little. I occasionally check Goodwill for aluminum bread pans and cookie sheets, as they have been my favorites. But, by all means, go ahead and make the bread; it's fine if you don't keep it in the pan.

I forgot how good that stuff is. We've used it at every restaurant I worked at. I should get some.

I'd never bought Barkeeper's Friend before, but dang if it doesn't work on nasty old pans. I bought a canister on a whim last month and by the end of the day I knew I'd be a lifelong customer.

And it cleaned my bathtub when nothing else would. My back injury means I can't really scrub a bathtub very well, and it also means I soak in the tub almost every day, so you can JUST IMAGINE the state of the tub*. A little BKF and a damp sponge brought off old layers of soap in horrible scrids and scrads. So clean!

* Please do not imagine the state of the tub.