I would say that your success with a handheld auger and the max size you could use would very much depend on your soil.
If you have very nice deep loam no rocks go big… might work… if you have 4 inches of good dirt and then sticky red clay filled with boulders like me… you would not get much more than 4 inches deep… or something is going to break… or you might get injured trying the handheld thing.