Requires a lot of trust in the unfeathering accumulator, or a lot of airspeed to get going with the starter. Would guess most piston twins used for training wouldn't meet required missed approach gradients and approaches like YMEN ils explicitly forbid it. I think students need to actually feather props a few times in different configurations (climb, descent, turns, approach, etc), to actually see the difference a feathered prop makes, but at a safe height (2-3k) with visual reference without the stress of IFR training. Engine failures in IMC can be practiced in the sim with feathering. After initial multi training and if the student is comfortable with feathering a prop, zero-thrust is more than adequate for circuit and/or approach training. Lots of accident reports to go along with that I think!