Some models, including the high-end In-Sink-Erator models, have a shield surrounding the top of the grind chamber.  The idea is that, if the flange in the sink isn't sealed properly, any water leakage will be deflected around the motor so it falls harmlessly into your cabinet (!) rather than getting into the disposer motor, which would be bad.

The top-end In-Sink-Erator models have "two-way grind", which apparently means the motor will reverse and run the other direction to avoid jams.

All In-Sink-Erator models apparently come with a special wrench, and a place in the bottom of the disposer to use it.  The wrench is really a funny-shaped Allen wrench.  The motor shaft has a hex hole in the end, and there's an opening in the bottom of the housing for inserting this wrench and turning the shaft manually.  The top-end In-Sink-Erator models come with a wrench holder on the side, but obviously you can use a clothespin.