I just upgraded from the Apple iWatch SE to the Series 11. The bands from the SE fit my Series 11, but the screen protectors do not as the screen is 2mm bigger on the Series 11.
I first bought the screen protectors as I literally smashed the screen on my SE when it fell to my travertine floor. Miraculously the iWatch still worked, but with the screen was so damaged I needed something for moisture protection and to ensure the screen didn't completely fall off. I limped along with the broken screen for over a year! I could not have done that without the screen protectors.
What I soon learned was that it was tremendously fun to "dress up" my iWatch with the screen protectors and bands. For every screen protector, I purchased a bling-y band. The compliments I get are off the charts - people are amazed that for about $25 (on average - $10 for a screen protector and $15 for a band), I completely transformed my iWatch into something very chic and elegant.
As I can't use the SE screen protectors - selling them for a song. Each are in excellent condition excepting the silver one, which is missing a few gems.
I have since replaced all my screen protectors with compatible Series 11 protectors - can show interested buyers the corresponding bands I have.