I did use one for a while but took it off when it got a bit marked and never put it back again. I used one that I cut to size from a generic camera screen protector film. Getting it on without bubbles wasn't easy, make sure you have NO dust. Check the sticky back of the film for dust too, not just the watch surface, which you will have washed and dried beforehand.
Washing and showering and swimming and sweating didn't seem to cause the film to lift even after 6 months. However, it never looked as nice as the sapphire.
Normal wear and tear (like doors) I'm not worried about but a bash against something like a granite boulder with lovely hard quartz crystals in it would probably cause me concern, even with the sapphire. If I know I'm going running somewhere like that I might put the screen protector back on.
Yeah, I know sapphire is harder than quartz, but so is glass harder than steel yet you can mar glass with a steel nail if you push hard enough... Maybe a layer of soft plastic might soften the blow a bit.
I did and still do use a rubber bumper around the watch sometimes, but it's more for protecting my wristbone against the watch than for protecting the watch!
