Hi Chuck
The theory is sound...
The failure of an engine is only infrequently as clear-cut as is the case when we simulate a failure. The clear cut movement of the ball to permit a "dead leg dead engine" diagnosis is not so readily apparent when the engines are developing lower levels of power, such as during an intermediate descent. In fact simply identifying that an engine has failed may cause problems under these circumstances
Similarly, engine failure on approach tends to coincide with the throttle movement that frequently accompanies the dropping of the final stage of flap, and at this stage, the margin of speed over blue line will often be minimal.
There are sadly a number of accidents in which the real-world problems of identifying an engine failure in precisely these circumstances have had a fatal outcome in types as diverse as the Seneca and the B737.
Keep with the theory, but don't overlook some of the real-world problems