I use a Hummingbird Matrix 37. I like it very well, I wouldn't go fishing without it. I have a quad beam transducer which will cover 40' of bottom in 20' of water. I can often tell whether the fish are there or not by making a couple of passes through an area.
I use my depth finder to look for specific structure like ledges, the old river bed (in the lake I fish), outside bends in the river old river bed, old bridge abutments, point dropoffs, and placed structure (brush piles). There often can be cats in these places. You can often find cats in the same structure bass fishermen find bass. I usually fish for crappie at the same time I am fishing for cats. I have found that if you find the crappie, you have also found some cats. The fishfinder is great for finding schools of crappie.
I am hoping to get a side scanning transducer for my unit next sping so I can scan banks and rip rap for cats. I also plan on getting a GPS attachment for my unit so I can mark waypoints and find them again. My unit already has a barometric sensor attachment which can help me decide where to fish for them and if they may be biting.
As I said before, after using my fishfinder for a season, I wouldn't go fishing without it.