I do both Reverse Hypers (technically you can do them over a high table if there's a counter weight) and Back Extensions.
I use both as a way to get some volume/assistance for my lower back. I would say neither is ''dangerous'', they're both great exercises that I combined with my lower body work. The truth lies somewhere in between, it's not dangerous and it's not a magic exercise either.
If you do any variations of Squats (Box, Front, Regular) and Deadlifts (Sumo, Trap, Regular) coupled with Back Extensions and/or Reverse Hypers + abdominal work (AB Roller + Weighted Planks are great) you're pretty much golden for all athletic purposes regarding lower body strength.