I have had a 27 model for the past year and it is a very good unit. I like the way you can add and expand it's usefulness as your pocketbook allows. It did take a while to learn the readings, but once you get it tuned in then it shows everything you need to see. I have the hookup for my hand held GPS but I have not gotten a chance to use it on the water. It is very easy to hook up with the wiring provided and removing the unit from the mount when not in use is easy.