It flies!, page-164

Yes, the unguarded blades seem to be a serious issue to me - it will only take one child to lose an eye and it could all be over, IMO.

I stopped buying any quad copters or helicopters without the a blade guard or ring a few years ago after I nearly took the eye out of my then 6 year old with a small indoor remote controlled copter, all due to my lack of driver skill.

Luckily I managed to avoid telling his mother about that one...