You will never have to worry about mold, mildew, rotting, rust, or any such problems, that are commonly seen if they are not cleaned every once in a while. Also, it need not be cleaned very often, just dusting it can make it look shiny. However, plastic furniture is not durable, sturdy, and can crack, easily.
Cast iron furniture is very heavy, but is more durable than other cheap and inexpensive sets. Iron furniture is versatile, stylish, and strong, and are available at reasonable prices, too. Maintenance is not a problem, as it is often painted or galvanized.