Has anyone used blackboard paint? Is it any good?

I've been toying with the idea of getting some for ages now. I'm thinking of using it for labelling containers in the outdoor area, as obviously home made labels don't last that long outdoors. I'm thinking of using it on big buckets/trugg tubs etc. Then I could rub out the label (chalk or chalk pens) as and when the contents of the container changed - rough and ready. That way, I can label things up with the children - thus modelling writing for a purpose.