My DIY carbon boxes add 330grams ,with bottom stringers included.Main reason is there is no big PU 80kg/m3 block.Since the loads are taken by carbon structures i can build direct into the XPS.
They are super stiff and remain stiff because they do not rely on foam for rigidity.
So the advantages in a tuttle for me would be hydrodynamycs and plate weight/stiffness.
Not sure the gains would justify new mast,new boards.
But i like the adjustable Tuttle concept a lot.So clean.