I bought 4mil from eBay sellers. There is no loss in clarity, unless you want that. Excellent UV rejection 90% VLT, virtually clear, blocks 99% of UV rays.
To put it in (I have it on all windows and doors in our house also), I first mix up 2 tsp of baby shampoo in a spray bottle and spray the window.
Then I use a razor scraper to scrape the glass clean, stopping about 1/8 of an inch from the edge of the window (you don't want to push the dirt into the frame).
then I wipe down the window with a lint free cloth.
I then spray the window again and squeegee it wiping the squeegee off every time. Now the window is clean.
I spray the window lightly one more time and then get the film ready. No dust around it I normally do it on a table that has been wiped clean. As you are pulling the backing film off spray the film so no static builds up. If it does it will attract dust/lint/etc. Now you put the wet film on the wet window. I take a plastic scraper and go over the film once, then I cut it to size. When using the scraper (like a squeegee) stop 1/8'' from edge. After it is cut to fit in the frame I then go back over the film with the scraper wrapped in a towel and really press.
Then its recommended that after it dries to go around and put some clear silicone over the edge so its connected to the frame.
How to apply Window Film - YouTube is one video I used to help learn how to do it.
Remlor 4 Mil Safety Security Window Film 30" x 25 Ft | eBay was the ebay seller I used. Very helpful.
Its not cheap but when you figure the larger mils are used for blast proofing and bullet proofing this is a bit of peace of mind. It was also part of our over all security plan.
I would say to start on a small window that is out of the way, that will let you get the mechanics down. Its not that difficult, just time consuming you do not want dust motes on your window being trapped where you can see them.