ppl will always be able to peak at your system thru the front windshield (unless you plan on using a sunscreen).
during daylight, 20% is still visable at sunlight but not during night. if in shade during daytime, it could be hard to see inside.
with 5% rear, i had little trouble backing out dark driveways/alleys/parking lots. i usually have to stick my head out the window and use the side mirrors. you'll get used to it though.