We had one for years on our charter boat in Lake Michigan. First one we had (if I remember correctly) was round and had a round dial on it. Colors where on the outside and it put a pinpoint next to the color of the day. Problem was, this was long before a ton of scientific information about how fish see color at depth. That and it didn't have a cord long enough to go deeper than about 20 feet. Great for steelhead, lousy for salmon and other deeper fish.
I could see it useful fishing in water less than 20 feet, but it was a worthless product on the big lakes. I can't remember one time when it put fish in the box for us or the customers. But it was always funny to throw it down, put the color on that it said, and then fish all day with it and never catch anything while a bait on the oposite end of the color spectrum slammed the fish!
I have OCD "Obsessive Crappie Disorder"