The Hammerite stuff is OK as long as you do the job properly.
Grind as much of the rust off as you can, then go at it with a really stiff wire brush.
Apply the Kurust, leave for 3 hours then apply a couple of coats of Hammerite black paint. It won't stop it forever but will last a good while.
People get a bad impression of the stuff when they just paint it on without any prep time. Do that and the rust will be back in a couple of week.