I have my nexus in one of those cases that fold up, and if you have a clipboard thingy in your van in the centre of the dash, I just open the case and hold the case in the clip , and the tab just sits there, never fell off and it doesn't viberateI have a Samsung Galaxy Tab and tried all mentioned and by far the best is Co Pilot .
finding a suitable mount has been my problem .. two that I've tried so far have been useless pieces of plastic crap..
Tablets are relatively heavy so need a substantiation mount ... The first one I bought you couldn't read the map for it shaking.. the second one was little better and it kept falling off the screen..
Before paying for Co-Pilot my advice is to find a decent mount, (if one exists) then try out Google maps and Navfree ..