Just returned from Trinity Alps, CA were the PN-30 really shone!
One thing I did find is that while I downloaded all of the "Color Aerial Imagery", the plain old USGS Quads 3DTQ maps paired with flag markers were MUCH more handy when you are on the water.
Scouting the rapids before by land then flagging the hazards made navigation more fun.
FYI I used the strap to wrap it to the thwart and left the unit on the floor of the canoe in the rapids and left it balanced on the thwart on flat water.
The unit gets a 10 however the 8 reflects how long it takes to download maps via Topo 8 and the super slow map server Delorme have.