I believe, there should be an inbuilt control mechanisme in the DHF. Devs should write down the effective hours that they work on a project and there should be a handfull of controlers, people, that double check the work done.

Yes. Absolutely. things can be gamed, but putting safety guards raises the morality alarms in their heads. "Will I cheat and lie like a dipshit or do i just work as promised".
No safeguard is perfect but its better than anything.

I believe that the DHF doesn't give an incentive to actually reach a finished project.

All good points.