I've always had matte screen MacBooks in the past so when I had to upgrade to the retina I wasn't happy about the reflection and glare. I had no choice but to add a screen film to reduce the reflection and glare.
I looked at Mosh AG also, but it's not affixed to the viewing area so I thought there might be some strange effects when you change viewing angles. This is theoretical because I never tried this item. The cost was also a factor - $40 for a piece of plastic is a bit much.
I eventually went with this product, $15 at Amazon...
http://www.amazon.com/Kuzy-Anti-Glare-15-inch-Protector-MacBook/dp/B00C2CRDJU
The challenge with this protector is applying it to the screen. The entire back surface adheres to the screen and it fits perfectly* within the rubber edges of the screen frame. Initial alignment is key to getting a proper fit. Getting dust and air bubble out from under the screen was another challenge. It took me about an hour but it works well and looks great.
It doesn't degrade the image colour or brightness nor does it cause any weird effects when you view the screen from a different angle. I believe they have a glossy one also. Most people that see my screen don't notice it, or look and go, what is different about it?
* when I say perfectly, there is probably less than 0.5mm of clearance on each of the edges. There is no reflection visible from any of the edges. The only exposed screen area is where the iSight camera is.
The poor reviews on Amazon are from people that could not align it or get the dust/air out from underneath. I've installed lots of these on my phones and tablets, but this was the biggest screen by far. It was surprisingly not as difficult as I expected.