What you say is basically how McGill advises to use it, support yourself on your elbows, keep a neutral spine, and stay in full control rather than swinging. The problem with that is you only get around 45 ROM and it completely defeats the purpose of the reverse hyper, you would be better off with RDLs/SLDLs/GMs. The way Louie says to use it involves a lot of spinal flexion but supposedly it also rehydrates the discs which would help recovery/healing.
What McGill says sounds more theoretical than anything, but Cressey has an article where he mentions chiropractors being sued by clients that were injured by the reverse hyper. I don't really know what to think at this point, I suppose that Louie's method should be relatively safe with lighter weights and people who are already injured are more likely to get more injured. Even if the spinal flexion does wear down your discs, is it not possible that the rehydration and hypertrophy would result in a net gain in back health? Lifting weights breaks down your muscle tissue but it recovers and gets stronger so why is this different?