When you think of metal and iron, you tend to thin that would be heavy for a mirror, but often it isn't and the metal might be cut out sheet and gilded metal, which many of the 20th Century sunburst mirrors are crafted from.
Iron mirrors may be salvaged architectural windows that have been converted into mirrors by adding mirror glass to the pane areas. If these are large, then yes, they certainly can be heavy, but they can be very decorative too. Very large ones can be leant up against a wall and used as dressing mirrors.
Reclaimed mirrors might be constructed from iron, or another material, but the term reclaimed is meant to denote that it is a frame for something that may have orginally been or had another purpose, other then a mirror. These can make for very individual, often one-off pieces to make your room more distinctive and exciting.
Tip: When hanging a mirror on a wall, you may want to ask an expert to do this for you. Mirror glass can be heavy and the larger your mirror, the heavier it will become and you need to make sure that it is properly secured to your wall. Ask the Dealer if they provide a fitting, as well as a delivery service.