Metal tongs, spoons, spatulas, etc will not hurt well seasoned cast iron if used in the normal manner. However, when I am making a roux in cast iron I do use a wooden instrument because of constant scraping and stirring of the roux.
One of the best uses for the square pan is frying bacon...all of the pieces will lie flat and not flip up on the ends like they will in a round pan. Obviously, square corn bread, and really just about anything you would do in a round pan will work in the square one. It works well for french toast too!!
Hope this helps....
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