I have only been actively crappie fishing for a couple of years and need to upgrade my fishfinder to a better unit. I have a 16' stick steering aluminum boat and usually fish the lake at Columbus, MS or on the Tombigbee river north or south of the lake. I have started putting out some porcupine fish attractors and the Hummingbird 525 is not good enough to consistently locate them. I am usually fishing in 10- 25 feet of water except when they go to the bank in the spring. I think a unit with GPS would be beneficial and have read the forums and should get as big of a screen as possible. I am 63 so a bigger screen would help with vision problems. I would like to find a unit under $600. Any recommendations