A key feature of torsion box design is that it provides a strong, flat surface while "minimizing" weight. For hand tool woodworking, this isn't a desirable feature in a workbench. The stability provided by mass will prove more suitable for hand tool operations, IMO. A thick lamination of MDF, 3 or 4 layers, will remain flat, given ordinary attention to the support structure. It will certainly be easier to construct, and dog holes can be placed anywhere you like. Don't expect them to keep their shape if used for hold-fasts, though. Even softer woods like pine or poplar give out quickly under the force applied by a traditionsl hold fast. Those screw-operated hold fasts might work fine.