I installed an InvisibleShield on my daughter's MacBook a couple of months ago. It doesn't look tacky at all to me, as you can hardly tell it's on unless you look closely.
I'd agree with anyone who didn't put it on the trackpad. It works fine, but it doesn't feel nearly as smooth as an unadorned trackpad.
I'm a very impatient person, yet I was able to install the one that goes on the lid. It took me three tries because I kept putting it on at a slight angle. When I pulled it off to try again, I expected to ruin it from stretching. But it snaps back to its original size. On the third try, it was perfectly aligned. Air bubbles do show up, but a credit card takes it out. Getting rid of bubbles is no big deal.