We have the Navman 5505 and yes its a bit small at speed, but you can blow up the display to include speed, heading and depth, or whatever you want on the screen really. A very usefull feature that means you can glance at it to see whats happening. When we first got ours, we found they did mist up, but then we stopped using the supplied white covers and no more misting! We use the navbus which you buy seperatly so that all the units `talk` to each other and display info on all the screens. Our charts came off ebay, whole NE coast for £70, so not bad. Found them to be reliable and good value.
Politicians, like nappies, have to be changed frequently - and for the very same reason.