Pro:
-Inexpensive
Cons:
-Ferrous metal, so sooner or later it will start to rust, especially filled with water.
-Some people (myself included) are particularly sensitive to the foul odor given off by galvanized objects while some can't even smell it.
-Many fish' senses include interpretation of electrical signals, and I don't know the long term issues with being housed within a ferrous object.
-Heavier than plastic (minor, but think about whether or not you plan on relocating it now and again)