I've been hit 3 times by rebounds off 8 yd targets... once in Swefta, once in FFTA, and once at CGC. One of them came close to my eye, but I wasn't shooting at any of them at the time...The eye one was on a plinking range, this summer. I spoke to the RO at the time and the target was moved closer out.
I can see them as a test, the variety of kill sizes used and the difference between 8-9-10 yds in trajectory terms can catch people out... but without wanting to be alarmist, I do slightly wince at them these days... I'm not sure whether some sort of baffle or coating on them is possible of if indeed the splashes came off a plate or kill.
Still, they do feel nice when they fall over, especially when you're having a bad day