If it works the way I think it does, the keyed collars are driven by the keys in the crankshaft, and the blades are driven by the small welds joining the keyed collars to the blades. Those welds should be stronger than the crankshaft keys, but easy to break each time you need to replace the blades. An alternative would be to omit the welds and drive the blades only with friction from the sides of the keyed collars, in the same way as Victa lawnmower blade plates are driven. I think I'd use the small welds, since I'd dislike opening up the cutter housing every five minutes to remove some slightly oversize piece of sapling that had become wound around everything.
With only a 5 hp engine, I see this as just a thin sapling shredder, not something you feed tree branches into.
