My garage door has windows across the top of it, which I've never liked because it's a security risk (anyone can look in the windows and tell if I'm home based on whether my cars are there). On the other hand, I do like that I can look out from my kitchen (door from the garage to the interior of the house also a window in it), so I was looking for a solution dark enough that you can't see in but I can see out.
I really didn't have high hopes for this window tint. I've always considered DIY window film a less than ideal alternative for people too cheap to pay for a professional tint job (think of all the cars you see with terrible, cheap tint jobs). But I decided to give it a shot, and if it didn't work out I could always take it off and either call a pro or rig up something else, as simply putting up some type of black paperboard on the inside would alleviate my security concerns.
I'm happy I went with this cheap alternative. I found it relatively easy to install. The hardest part is cutting it to the correct size, but to be fair I cheated in this respect because I was able to completely remove the glass panes from my garage door. By removing the panes, the film was easier to apply and because the trim would cover the outside edge of the window, I had a large margin of error when it came to trimming the film. If I didn't have the luxury of removing and replacing the trim around the window and instead needed to cut the film perfectly, it would have been much more difficult to do properly. I found it very easy to get the bubbles out using the squeegee and spray that came with the optional installation kit Gila Complete Window Film Application Kit. Make sure you have a sharp razor blade, as I wasn't very happy with the cutting tool that came with the Gila kit. A fabric cutter would probably make the job easier.
The darkness is about exactly what I wanted. It's now very difficult to see into my garage from the outside as long as the interior light isn't on, and the black film goes well with the black trim on my house. At the same time, I can still look out from my kitchen and see if a car is pulling into my driveway.
While I used this black film on my garage door, I also used a frosted film, Etched Glass Window Film 24-by-36-Inch to cover glass on the side door to my garage, which also has a window. I was happy with this product as well, as it also blocks the view into my garage.