What advantage does porcelain have over a plastic washing machine drum?

None. Porcelain is a enamel baked onto to a steel drum. It is hard, durable and easy to clean but can be chipped exposing the steel of the drum which if left unnoticed will rust and may leave difficult to remove spots on clothing. Touch up enamel is available but prep and application instructions must be adhered to. Plastic is is also durable and easy to clean but could become gouged (uncommon) where it will pick at the fabric of clothing. Some fine sandpaper will remedy this.

== == They used porcelain sinks, bath tubs, etc., up until around the late 1950s. They are high quality and I love them! Unfortunately, plastic has it's uses, but I detest plastic especially in washing machine drums, fridges and knobs on stoves. They don't take well to heat change such as from hot to cold and will discolor to an ugly yellow. I didn't even realize you could get a porcelain washing machine drum. If you have it or thinking of buying one then guard it with your life! LOL