I bought this product online along with my Macbook Air 13" and I realized after the order was already on the way that this was specifically for an 11". So when it came I didn't open it, just took it to an Apple Store to replace it with the correct size. However, when I got there, a sales rep informed me that both computers, though different sizes, have the same sized keyboard and so it should work on mine. I rolled my eyes at myself for taking the kind of long trip to the store for nothing, got home, opened it, and applied it to the keyboard. Where it didn't really fit.
The general width of the cover fits, yet, but the keys are different sizes! The spacebar on the cover is too thin to fit mine, along with all of the other keys on the top and bottom row of my keyboard. So now it doesn't fit at all and I can't take it back now because it's been opened. So I'm stuck with this thing that doesn't fit.
I'm sure the cover works very well for an 11", just don't let anyone convince you it'll work for both sizes! It doesn't!
The image used to show the product made it look like it protected the palm rests also (which it does not). The keyboard cover is a clear, rubber mold that is set over the keys - no adhesives. It does the job, but it feels like it could be a tighter fit. Using the keyboard feels spongy with the protector on, and the protector is very noticeable to me. Hopefully, over time it will settle down over the keys more as it has a tendency to rise up a bit when typing on keys at a fast rate of speed (90+ WPM). Overall, an average protector - probably over-priced for what you get in my opinion.