I have decided to upgrade depth finders. I don't want to spend over $500 but I want a decent unit. I have been looking at the new Lowrance Mark 5x with down imaging that Bass Pro shops has. Can you provide me the pros/cons of down imaging. I need it mainly for locating structure in tributaries off Ohio River. It will be used for targeting crappie. The unit I got is a cheapo Lowrance that came stock on my boat. Thanks.