I've got to agree with DHA on this one. It was actually guiding out of Weigh West in 1997 that convinced me. I was more than sceptical about the black boxes I saw on the boats of the more experienced guides and in fact, I put both feet deeply in my mouth mocking them.
About my second week there the bite was totally on for pretty much every guide at Portland Point except me. I kept hearing radio conversations between fellow guides talking about "cranking the box up to 7, they really want it hot!". Of course I had no idea what they were talking about and kept changing gear to no avail, but found out what was going on when I got back to the dock. The fish needed a "hot" `positive charge off the cable to get them interested that day. According to the other guides, all you had to do was crank up the box and the bite came on. There I was skunked, no tip, and pissed off guests. Needless to say, I put in a request for a black box the next day and haven't looked back since.
Now, its not always that simple, but I have had a few days since where it seemed that the charge off the cable made all the difference. In most cases, a black box will make sure your boat isn't repelling fish.
DHA is right - the technology was developed by commercial fishermen. The correct use of a black box is not simple and if you screw it up it can cause more harm than good. Read the manual!!!!
Bob