I put one of those on my screen and it makes a huge difference -- no fingerprints, and the glare is a little bit less. I don't find the clarity of the screen nor the sensitivity is affected. It also gives a slight bit more friction for your finger to give a little tactile response vs the naked screen. If you've ever used a similar screen protector on your iphone you'll recognize the difference. Not this isn't like the invisible shield/paint protection films - it's more of a firmer plastic film.
The film is a bit of a pain to get in perfectly straight due to the size and the screen below going nuts as I touched the front surface to smooth out bubbles or repositioned the film. The new screen cleaning mode in version 5 of the TeslaOS will be quite welcome for this.
A nice bonus: when I ordered it, I got 2 matte protectors for $25, but the company just emailed me to say they're sending another 2 of their new glossier films for free because the newest listing on amazon includes 4 protectors (2 gloss & 2 matte). I thought it was a generous offer since I still felt the original 2 pack was a good deal.
Given how many people want to check out my Model S, it's nice to not worry about the smudgy screen!