To wormery or not

I'm thinking of putting a wormery on my plot. Can anyone advise how much cast they produce and would Ineed more than one ona 8 pole plot?

I have just decommissioned a wormery and set the worms loose to free range in my compost bins. Not a lot of worms casts (which end up in ordinary composters if there are worms in there anyway) and not a lot of worm juice either and not convinced the worm juice is all that magical.

The wormery will make a good Comfrey and nettle tea vat next year.