Personally, I'm not too interested in these types of units - for now. This is an area of intense technological development... and these will IMHO hit obsolescense very quickly.
So, instead, I use Microsoft Streets & Trips, which has no route directions whatsoever (the 2006 version has an arrow for directional purposes, but that's all). All you get here is a map, and you have to draw line son it to determine a route in advance.
This actually works for me - for example on business trips I know the destination in advance and can follow a pre-drawn route while in my rental car. After an "incident" of getting lost on my way to a customer, I had been looking for a GPS unit for years when I encountered some earlier software... all of which had fussy GPS requirements and quirky software. That is past history, since now S&T can even come (optionally) with a GPS unit. I haven't been lost since... this is invaluable.
I also use it to plot drives that I lead... I have a "master" map with interesting routes in Central Texas that I can pull from. As some of you saw in the recent Solstice drive, I can lead the drive using S&T and make any changes necessary in real time - as well as estimate arrival time at the end. Again, invaluable.