I'd never used one up till a few weeks ago, used to play the waiting game, or in extreme cases, smoke em out!
One of the boys who I go with got a ferret collar for his dad's terrier locater, (mk1, I think) we slipped it on my jil and sent her down the hole. After about 10 mins of no bolts & no ferrets, we found she was in one place, not moving at all. A quick dig in the ground later, we had both the ferret, and a nice sized rabbit for the pot.
Me and two of the boys, are going to buy one between us. I think it will be money well spent.