I read a bit about PolyWatch, and my understanding is it does not fill the scratches but instead is like a liquid sand paper and by buffing the medium into the plastic face it buffs out the scratches. I also read some reviews on Amazon where other Tamagotchi owners said it worked for them. So I decided to give it a try.
Sorry, no before and after photos but for me it worked very well and I recommend it. I had bought a used V1 off eBay. It looked very good in photos, but upon arrival it had complete minor surface scuffing all over the screen that would not show in a photo. The screen should be a bit shiney, smooth and reflective. The one I received had minor surface scratches all over and the screen looked dull and not shiney or reflective. I applied a dot of PolyWatch to the center and wiped/buffed a dozen times. After about 6 passes it looked fantastic, but I did 6 more passes to see about clearing the few minor nicks that were left. My tama now looks excellent quality with only a few barely noticeable scratches as most used tamas may look.
The directions say to apply pressure when buffing but when I do that the screen pixels get activated. So I did not apply as much pressure as they may recommend, but it still worked great.
I used a cotton muslin washcloth to buff. A cotton swab or lens cloth would probably work well too.