Unlike heme (animal) iron, elemental iron is extremely toxic to the body.

I recommend against cast iron for pots where you would boil liquid in them, or for grilling grates.

As a frying pan, where a deep fond builds up, or with ceramic coated, I think cast irons pans can work. Personally prefer high carbon steel for pans for heavy duty searing.

Nickel in stainless is also problematic, as nickel has a long half life, so it builds up in the body. Women with PCOS almost always have a high nickel burden. It's not benign.