MFCREW,
As a CSD, I would not allow my crew to take rest in the Club or First cabin.
Unfortunately, CSDs have been reported in the past for doing such, so it is just not worth it.
At the end of the day the CSD is accountable for such actions and therefore risks getting into trouble, facing possible suspension.
It might be seen as a 'perk' to some but the cabin crew who might enjoy their rest in a First or Club seat don't have to face the risk of being reported.
Our agreements require us to have horizontal rest provided on a box 2 and above. Horizontal rest on any other flights is a bonus but not a requirement.
Besides, what impression does it give if 8 crew take their rest in a cabin with fare paying customers in? Not very professional.
My opinion, of course.