I've had one for about two years now. Here's my experience.
1. It was quite an expensive thing to buy - just over £100 for a complete kit.
2. It started off well, using the supplied worms and their 'bedding' (that they ate). But then it started to grow spectacular mould on top. I contacted the supplier and they could only suggest making sure it was sited in a well ventilated area and to turn the food stuff over. That didn't work and after much inspection over time I realised that it was pieces of bread and cooked veg (eg left over potatoes) that was the problem. So only put raw stuff in there, even if it's all veg.
3. After that things settled down but as someone else has said, it's pretty slow to work. Don't expect to get rid of loads of kitchen waste quickly.
4. Even when the lowest layer is ready to be removed, it doesn't produce all that much compost. Although it does produce a lot of worm juice.
5. I can't find anywhere that describes the actual makeup of the juice, only statements like ' dilute 1 to 10 for great plant food'. I tried feeding it to my tomatoes this year, then gave up when I realised that the plants just weren't thriving and started to drop their flowers. After about 10 days of using proper tomato feed, they recovered really well. So I won't be doing that again.
Conclusions?
A wormery is useful if you want to avoid having to give moderate quantities of raw kitchen waste to the refuse collection. It does not work very quickly and produces only small amounts of (very wet) compost and a fair amount of juice, although I have no evidence of how good that is. I will continue to use mine for now but I may decide instead to use a compost bin that I'm building for my new allotment. If I'd had the opportunity to see a wormery in action, over a period of a few months, I would probably not have bothered. I've read on the web about people who build their own bigger ones - they say the proprietry ones are simply too small. Google for wormery and see what you find.
Good luck.