It is very important that the manual extension handle is properly stowed. The Cessna 310 has exactly the same gear extension system except the manual extension handle is located at the front base of the pilot's seat and I have seen the results on one where the handle was not latched.
The system is basically one large gear with two smaller gears that engage with it. One of the smaller gears is driven by the electric motor while the other is connected to the hand crank. As mentioned above, extending the handle disconnects the electric motor gear and engages the hand crank one.
If the handle is not correctly stowed it is possible that both smaller gears will be partially engaged, that is neither smaller gear is fully engaged across the whole width of the larger gear. When the electric motor is engaged to raise or lower the undercarriage it will strip several millimetres off the teeth of both gears. The cost of replacing the gears is astronomical.
It is why the checklists for both Baron and 310 have an item in the pre-start that the emergency gear handle is stowed. I wonder how many people actually check that it is?