Welcome to Crappie.com. You came to the right place to find out any and everything about crappie fishing. They are a lot of people that know way more than me but I will give you what I know. The SI sonar is a very valuable tool for finding everything in shallow water and the GPS will let you pinpoint what you find and go back to it. The DI sonars are also very useful for seeing the structure and fish and with SI you normally get all three sonar views The bigger the screen on the sonar the better especially if your eyes are old and not so good like mine. A good sonar is well worth the cost in my opinion.