I've have bins similar to that have lasted for close to 20 years. They work very well. I recommend you get at least two, more if you produce much for compostable green waste. Once a bin is full, you set it aside and turn it weekly or bimonthly through the summer. The more aeration it gets, the faster it's going to decompose. While it's not necessary to keep it covered in the rain/snow, it's not a bad idea so that it doesn't turn into a bin of mud, particularly if it's getting to the point of being usable or if you're going to screen it.
As to the worms, yes worms will help break down the material, but there's no need to add them, they'll find their way in as the heap is made and does it's thing. Worms will not stay in the bin once it's been transformed, so buying them is a waste of time and money.
Last tip: Keep the bin on bare ground, this way it will allow the worms to migrate in as well as allow microbes in.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!