The main problems with the grub screw attachment of an auger is two fold, first you need a few collars to suit tge auger shaft diameters. These are often lost and you need to get new ones machined up. Secondly the grub screw, they get mangled, stuck through saw dust, rust etc. and if you haven’t ground a big enough indent in your auger and it spins, your in a whole world of hurt potentially getting everything apart again.