Haven't had a boat with one, but have seen a number on other boats and have been impressed with the 952. The 667 is a great unit, but if you are looking to buy, would suggest you go with one of the lcd units like the 582 (now 585). If it's already on the boat, the more important question is the transducer. The unit can only work as well as the transducer to which it's connected.
I had a 667 on a previous boat and it is a great unit. However, the screen is tough to see in the bright light. It is also a big bulk unit. Go with the newer LCD screens