Everyone
The differences between the DHC-6 TwinOtter and the Beech could just be in the certification process - DHC had to be certified to the Canadian standards while the Beech was certified to the USA standards.
Also the TwinOtter is missing the Weight On Wheels system - many aircraft spend a good portion of their life on floats - so possibly this is the reason for the different interconnects that needed to be made before allowing the power lever into reverse. IIRC the TwinOtter had 3 things that had to happen - prop lever fully forward, flaps selected and in the approach position, and activation of the twist grip to get the power lever below the flight idle position. It is easy to get into reverse in the air with the TwinOtter - and no it is NOT APPROVED!!!
I have some right seat time in the -6 and one of the things that was my responsibility was to follow up the captains big paws on the power levers on takeoff and to maintain positive forward pressure on the propeller levers on the landings. My left hand stayed on the prop levers right from the "Full Fine" command from the left seat. By having clearly defined cockpit procedures it eliminated the uncertainty of who was doing what.
Many other aircraft require the weight on wheels system - ie "Squat Switches" to indicate the aircraft is on the ground before allowing the power lever below the flight idle. At the end of the day it really doesn't matter what system is being used as you are trained for that specific aircraft type.
Regarding the propeller action when on the Fuel Topping Governor - All mechanical governors "Hunt" during operation. I use the word hunt rater than cycle because to me something that cycles turns on and off while hunting is the variations in speed (and torque) within a narrow range.
One of the maintenance checks that can be done is a check of the fuel topping governor speed. This is accomplished by the removal of the air bleed reset link to the integrated governor and locking the fuel topping governor reset arm to the reverse position with lockwire. This has the effect of simulating the operation of the fuel topping governor in reverse but operating the engine in the forward range. It has been a while since I have had to do this but I don't remember the propeller cycling but I do believe it will hunt a bit more due to the little bit more lag in the system as we are controlling the propeller speed by changing fuel flow from the FCU.
What does cycle is the Beta Backup System - or equivalent. On that system you can see and feel the cycling when you do the ground test. The operation of the ground test simulates the system in flight mode while on the ground. It changes the logic of the power lever below flight idle switch to indicate flight mode. So with the switch in the test position bringing the power lever below the flight idle detent will drive the propeller blades to the low pitch sensor. The sensor will activate the system which sends an electrical command to the lock pitch solenoid. The lock pitch solenoid will close blocking off the oil flow to the propeller and the propeller blades will now move towards a greater blade angle. Once moved to the point where the low pitch sensor is de-activated the electrical command signal is removed from the lock pitch solenoid. This allows governor oil pressure once again to the propeller which causes the blades to move towards a lower pitch and the cycle starts again. You can see, hear, and watch the indicator lights come on and off as the system cycles.
Regarding a propeller system failure and ending up with the fuel topping governor in charge I would be very irresponsible to suggest anything other than what is written in the flight manual. There are too many variables to consider - follow the checklist is the only advice I can give here.
Hope that helps!!