Anyone use one of those plastic "Screen protectors " on the rear bumper?

Try Priuschat Store's Toyota OEM black plastic protector. They are generic Toyota scratch protectors made to fit multiple Toyotas and they fit the Prius well. I had one on my Gen II and now have one on my PiP. Design is well executed; the part looks good on the car, a slight crease along its axis makes it easy to locate onto the bumper during the install, and I've never caught any corner of it while loading & unloading lumber, luggage, trash, metal recycling and woodshop machines over the years. The material is "bendy but tough" and the one gouge that I caused is practically invisible and didn't go all the way through. Cost was around $41. Two-minute install with no tools and you're done for ever.

 

I think the rear bumper would be a compound curve, making application tough, requiring slits, depending on how flexible the film is. How does the film hold up over time, say if it gets a bit chewed by someone's license plate bolts?

My 2 cents: leave it bare, take your knocks, and if it gets bad get it redone by a body shop, occasionally. It's pretty much guaranteed as soon as you do get it redone you'll acquire some fresh dings.

Just a bit of a rant: today's cars by in large don't have bumpers, they have fairings. Our first vehicle was an '81 Civic. I know, not too pretty, but the bumpers were steel with plain black rubber casing, mounted on hydraulic dampers: