One advantage of a fixed mount unit is that it's fixed mount. E.g. if you want to hear the music while running in sloppy stuff, it can be hard to keep a moveable unit from falling off the dash, table etc. I used to use a portable, rechargable stereo/ipod dock in my 22. It worked great for slow cruising and while at the dock, it wasn't so good for motoring out to the fishing grounds or to listen to in the cockpit while fishing in the rain. For those purposes, a fixed mount with marine speakers is better. It all depends on the intended use.