the greyscale units are more than fine. there isn't anything a colour unit will show that you cannot see with a greyscale one. bottom composition, schools of baitfish, game fish, etc. the color units may be more easier to grasp at a glance. what is more important is pixel count. this will determine how detailed and the level of separation between what you see is. ie. show you fish on the bottom as far as downscan, i have not used it but it is NOT a replacement for traditional sonar. do not get a DSI only unit as your only graph.