I have the Hercules which uses the #3 cutter and has a 5/8in square shaft. At the time the Osprey was not available.
The Osprey is available in #1 cutter / 3/8in round shaft or #2 cutter / 1/2in round shaft.
You may prefer a round shaft, slightly easier to roll on its side for shear cutting.
I do not know if the smaller cutters perform any different than the larger cutters.
I am on my second #3 cutter. Already had a small chip so had to rotate to a new area.