Can't help you with the 500, but I have the DS400X on my boat with a transom mount. Personally, I love it. I have no trouble seeing fish, bait, etc. Since this was my first color unit, it took a while to learn what I was looking at. But once it was explained to me, everything was a clear as day. Very nice unit. The one drawback with the transom mount is the plastic mounting bracket. It has a snap into place feature. Last year when my boatyard launched the boat, They hit the ducers with the forks and popped it up. Of course, this is what is supposed to happen in case you hit something in the water. But what a PITA to get the thing locked back down with the boat in the water.