I love the Rome 1705 (I also have the double rectangular one, the 1605).
Actually, your cast iron pie iron needs seasoning before use, too. I seasoned mine at home on my Weber grill. Because pie irons are smaller, seasoning one seemed (to me) to go faster than seasoning a larger piece of CI, but YMMV.
I suppose you could just seriously oil it down, but I'd take some time and season it. If the 1705 screws off the metal/wood handles, you could also easily do it in the oven - basically set it and forget it for a couple hours.
Because it's square, and most bread is square, the 1705 won't "crimp" quite like a round pie iron crimps regular bread, but ...
YES, you absolutely can use pie crust, pop-can biscuits, phyllo dough, puff pastry or bread slices wider/longer than the iron, and your pie or sandwich will "seal."
I've also used portabello mushroom caps, bacon slices, or wide thin strips of eggplant or zucchini, overlapped to make a solid base and top, with a filling of tomatoes, garlic, onions and ground lamp to make a breadless camp meat pie (or you could make an all veggie pie if you wanted.)
Since I'm a single camper and like to travel (relatively) light, I have been known to take a minimal kitchen kit that is just my square and double pie irons, a coffee pot, a deeper pot to cook soups/stews, a wooden spoon, tongs, cutting board sheet and a good chef's knife and call it a day. Pie irons are very versatile little cookers, and the Rome 1605 double rectangle can be separated and used as two small skillets.
Simple recipes from the Rome company will explain exactly how to use bread in your new square pie iron. Enjoy it!
