Tumbarello, what you say depends on if you see article 3.17 of the regulations as a description of the application of the rule described in 3.15, or as a separate article. To me, 3.15 is a separate article as it describes different constraints to those tested under 3.17.
For the F-duct, you have to admit that no other solid device on the car than the hand or knee of the driver moves when it is toggled on or off. So as such, there is no movable aerodynamic device. No matter the intent, the letter of the rule is respected.
The bendy wing does breach regulations, if only regarding "attempts to bridge" the contact to the ground described in 3.15. The wing is clearly designed to get as close to the ground as possible, and sometimes makes contact with it (as proven by the wear on the RBR endplates last weekend). So if only in that one respect, the rule is breached. Not rule 3.17 about bending bodywork. Rule 3.15, a different one.
Now for the advantage estimation, I doubt an 0.5 second interval is anything precise, especially in Formula 1. It's a ballpark estimation, an educated guess coming from the feedback from numerous sources about advantage for ground effects and some years of experience in fluid dynamics. Nothing more. But if there was no advantage in it I doubt Red Bull would bother. Newey is smarter than that.
Again, I don't think RBR are the culprits here. I think the fault lies with the FIA, who seem incapable of writing rules which would be clear cut for all teams, not interpretable by one or two in a different manner than the others.
And in that point, we come back to the slot/hole discussion on the DDD. A proper racing rule should not be subject to interpretation, and the FIA need to clean up their act or let someone else do the job.