It is a very simple install. If you're doing it by yourself, i'd put a pad on the roof for protection. That let me rest the one side of the rack on the roof while I started the install bolts and shims on the other side. Another pair of hands would help, but not neccessary.
They are fixed in position using the existing holes in the racks. Check out the location of those holes NOW before you order and make sure you can live with this position. If you want more flexibility, aftermarket is the way to go (some pics in gallery).
One thing that sold me on Nissan racks were the fact that they were flush with the side rails when installed. This helped keep the side profile low.
This was the very first part I bought for the MO - along with the bumper guard. My dealer in Hawaii didn't even know these existed. I found them thanks to this forum. I ordered from Courtesy, very fast and professional service.
I have 2 car seats in the back full time and they are a hassle to take in and out. I put 2 full length rack pads on for protection and I've been hauling everything from kayaks, surfboards to folding tables and 2 x 4's. Helps prevent something nasty messing up your interior.
Great investment IMHO. MO_808