I purchased this to use with my Pentax K-x camera. The installation took less than a minute and I was very surprised when I looked through the viewfinder the first time. It definitely makes it easier to focus manually. I purchased another piece of focusing screen with a double prism but I didn't like that and removed it.
I was a little hesitant purchasing this at first since I wear glasses but it hasn't really limited what I see through the viewfinder. I definitely recommend this.