Installed mine a couple days ago. It went up pretty easily. Although, it would have been much tougher without my wife's help with a second set of hands when actually putting it up into place.
First, stopped by the local hardware store, one of the best I know, Fresno Ag Hardware. I picked up a roll of plastic liner and some adhesive spray. I cut the rough edge off the end to match the width, then counted the ribs in that width to figure out how much to cut off along the length of the roll.
Put some painter's tape along the edges to protect them from the adhesive spray.
I didn't spray any adhesive on the rear (of the vehicle) portion of the shelf. This allowed the matting to be pulled up so the center screw could be accessed to install it. After the install, I used some double stick tape to keep it in place. I trimmed the ends after the adhesive did its job.
Only issue was caused by me. While putting the adhesive and matting on, I left the shelf perched poorly on a work bench and I bumped into it and it fell off onto the cement. It tweaked a bit on the passenger side (mostly), but it did so in such a way that it really isn't noticeable.
I'm really happy with it. My glasses, camera, GPS (when not using it), misc stuff, and iPad2 in its case fit up there very well. Keep in mind, this shelf is designed for lightweight use, six pounds. (Think 5 lb bag of potatoes, plus a pound--not bad.) You can't use it for a shotgun rack or any heavy equipment. But for the light stuff that you often throw on the other seat when there isn't a passenger, its great.
Years ago when I was big into the mini-truck phase, I had a new 1975 Chev. LUV pickup I tricked out. I was working at a lumber and hardware store at the time, and built my own visor shelf from stuff we sold there. It turned out to be a real pain to make. This was much easier and worth it for me.