Greentext

It's pretty likely that the temperature needed to polymerize the oil would destroy whatever compounds are responsible for making olive oil taste and smell the way it does. Plus, if done well, seasoning creates a permanent bond between the polymer and the metal, so you probably wouldn't get anything to come out of the seasoning into the food.

As for adding iron to the food, you might be thinking of acidic foods causing iron to leech out into the food. If the seasoning is "perfect" then this might not happen, but any weakspots in the seasoning can allow acids to corrode the pan if they're left there long enough. Common advice you'll find is to avoid cooking acidic food for long periods of time (e.g., simmering tomato sauce for several hours)

Olive oil works well for seasoning, idk about taste though. You burn all that stuff away and what's left is bonded to the pan so there's not much room for flavor to transfer.

Grapeseed oil.

Cheap at big box stores. Incredibly high smoke point. Dirt cheap.

Use that for first couple layers and after that honestly whatever oil or fat you want to use or have. I re-up my pans with everything from Crisco to just cheap "vegetable" oil (rapeseed or soy usually) and even duck fat from after making other dishes.

Don't expect any to necessarily be more delicious but sometimes you get different flavors from what sorta burns in. You supposedly might get some iron passing through but it's actually kinda a necessary mineral like volcanic ash.

I use whatever is on the counter usually, but lard (homemade), bacon fat (clarified) and avocado oil are the usual and seem the best when doing the high heat seasoning. I just get the pan hot after cleaning it, with a very thin layer of oil (wiped as thin as possible) and keep wiping oil in there awhile with a paper towel, take it off the heat and occasionally wipe it with the paper towel to spread it evenly.

Pancakes also work as pan rehab. The long low heat works to get them smooth again. I use butter for that, which leads me to believe that any fat is probably fine.

Avocado oil is what I use. It has the highest smoke point of the readily available cooking oils, is supposedly healthier than other oils, has a clean flavor and doesn’t peel once polymerized for me. Olive oil works, and so does various other fats; bacon, tallow, butter etc.

I use my cast iron more than any other pans because it is more versatile than my carbon steel or stainless steel pans. Each have their own place but cast iron works for more of what I do. The cast iron absorbs heat and works well for doing high heat cooking so having an oil that doesn’t burn until higher temps gives more temp ranges to operate in. When an oil/fat goes past it’s smoke point it becomes a carcinogen and is unhealthy to breath/eat. So avocado oil’s smoke point just over 500° is better than olive oil at around 300°-350°f.