From the aopa training website, sums it up pretty well..
Although Bendix drives were phased out of the automotive world in the mid-1950s, they are still standard equipment on some new airplane starters. However, the B&C Specialty Products starter uses a linear actuator, and the Sky-Tec starter uses an electromechanical actuator to replace the Bendix drive. If the engine doesn't start, the Bendix stays extended, meshing tooth-to-tooth with the ring gear. An extended Bendix can create problems if hand-propping is required.