I had it on my iPhone for about 6 weeks until I had to take it off to make the phone fit in a case. I think Invisible Shields are easy to install, I've installed dozens myself (for friends and family), but I must admit the sides were a pain because they slide around too much on the aluminum during installation and it is difficult to position them correctly.
They look fine until they start to yellow which happens fast. I didn't think it was particularly worth it, IMHO. I have the Invisible Shield on the front and back and I love it, but I would never reinstall the sides.
P.S. Not many cases will fit if you have the sides installed!