Correct. The case does not flex sufficiently to cause failure. The ONLY research showing this might happen, was done many years ago with extremely unrealistic boundary conditions (both shafts locked together, no engine bolted to the bell housing, and in steady-state loading). Even then, the case deflection was marginal and not nearly sufficient to cause the shafts to separate. If you look at the basic design of the gearbox, and have any understanding of engineering, you would see the lack of logic in the case flex claims.
But, people are eager for a snake-oil charm and are willing to believe whatever they will to justify the money spent, just like every other brace people think they absolutely need. You spend the money, know "this thing is gonna blow and is only held together by these plates", and drive more carefully as result.
PayPal me half the money, and I'll send you a PM once a month for the next year reminding you your trans isn't bulletproof and that you should drive accordingly.
I really like the guys at Moore, and they build some of the best parts I've seen in the industry. These plates are no exception. They are likely built exceptionally well. But if you think they are going to bulletproof your trans, you are fooling yourself.