I haven't been playing with sims for some years now so I'm a bit out of the routine loop there.
However, the DD (or similar) system is fine in principle.
One concern I have is in respect of engineering (ie certification) rigour. For instance, my understanding is that the Australian military system's process permits an ad hoc approach to some extent .. I am told that there have been a few unfortunate stuff ups probably due to a lack of engineering rigour in the assessment for CFU (ie DD) status.
However, the basic idea is pretty fine.