Don't get me wrong: these are very good at what they do. Quality-wise: there are definitely better screen protectors out there. I've seen protectors that enhance the sharpness of the Kindle's text, virtually eliminate glare - stunningly useful stuff like that. The catch is that they're about 5 times the price. These will have virtually no affect on your Kindle screen be it positive or negative.
These are bog standard screen protectors: they protect your screen. End of story. I'm giving them 5 stars for being exactly what they claim to be, and being good value for what they are. Also: screen protectors are not easy to attach perfectly to a Kindle, so having 5 spares is no bad thing!
If you want better, there is definitely better out there. But as far as it goes, these are all you really *need* to keep your Kindle screen scratch free.