Gee I always demonstrated and observed full feathered landings. Remember you ,the instructor, knows this (the m/e trainer) aircraft like the back of your hand. Yep, sure many times there were "goof" ups but nothing you wern't expecting nor could get out of.
After the war many newly graduated RAAF pilots who had only ever flown Tiger Moths and Wirraways, were given their initial multi engine training on the four-engine Lincoln bomber at Amberley, Townsville and some at East Sale. Keep in mind this big bomber was a wartime tailwheel design. The conversion course included practice feathered prop landings and go-arounds.
Several of these aircraft crashed (two at Townsville alone) during asymmetric training with prop feathered. The flying instructors of these aircraft were highly experienced pilots yet they stuffed up. RAAF HQ realised they were losing more Lincolns to practice feathered landings than in day to day normal operations and directed that in future practice feathered landings were prohibited. Zero thrust approach and landings were substituted instead. The same applied to all RAAF multi-engined prop aircraft. The accident rate went to zero.
Draw your own conclusions.