Rats will eat their way through the plastic basket in the bottom of the standard green cone. If you buy direct from
Green Cone Ltd, you can specify a wire mesh cage to go around the plastic basket.
If you get one from your local council at a subsidised price, then you don't get the wire mesh to make the cage. However, when I contacted the manufacturers, they sent me a new plastic basket and the wire mesh - free!
Details on how to stop the rats can be found on the Green Cone FAQ, but when I mouse over the link on the website I can't quite click on the FAQ link. Hopefully others will be able to get to the page.
As for the Green Cone, we've had ours since the end of last winter and so far it's working fine. We've positioned ours between two apple trees, in front of a south-facing stone wall and it gets quite warm when we get the occasional ray of sunlight. Animal fats, egg shells and the like are all breaking down well. Winter will be the real test.