Leeches as hook bait

Read an article some time ago on how good leeches were as Carp and Cat bait (article was mainly on Cats) just wondering if any one on here has tried them and with what success? There was a link to a company selling them but they were bloody expensive as they were being grown / developed mainly for medical purposes!
John.

Have not tryed them but leeches and raw liver are ment to be fantastic for catfish but also good for carp.