Wormery

I had one, but in the end I gave it away and released the worms into one of my compost heaps.  There are pros and cons.

They do make a rich dark compost/fertiliser, but it is quite a slow process.   They also make liquid feed and you get lots of this. They are better placed under some sort of shelter to keep the rain out and protect the worms from the extremes of cold and heat.  They are active for more of the year this way,

If you want lots of bulky organic matter for using on your plot, a compost heap is a better use of space.  If you want some premium compost and lots of liquid feed, as an addition to your normal composting, they are great.