I picked up a roll of 5% mirror tint on amazon.
Its slow going putting it on. My wife helped a lot, I'd cut it to rough size and she'd spray it with baby shampoo and water while I pulled the clear plastic off of it, then she's spray the window down and I'd put it up there. Then she'd smooth it out and trim around the edges.
Go slow and take breaks. We ended up re-doing a window twice and still screwed it up because we were getting worn out and made mistakes.
I'm REALLY happy with the results though.
Window on the left hasn't been tinted yet:
Its nice we don't have to draw the shades to have privacy. No one can see inside, and even at night with all the lights on inside, you still can't see in unless you get within a foot or so of the window.
The day after we installed it, a girl camping 2 sites down from us came and asked if my daughters could come play. They were taking a nap, so we said no. After we closed the door, I watched her walk away, then double back and steal a container of playdough from my girls' toy bin.
Went and got it back and had a very interesting conversation with her mother.
I don't think she had encountered a 2 way mirror before.