Maybe, as you say, killing the engine with the key or kill switch instead of the decompressor like many recommend is safe.
Maybe doing this won't kill the sprag clutch.
Then again, maybe you guys have just been lucky.
Envision this scene:
The engine is running and suddenly the ignition is turned off.
The crankshaft has enough energy to shove the piston up on a compression stroke and gains some of it back as the piston decends from TDC on the now, unpowered power stroke.
This action, coupled with the energy remaining in the crankshaft runs the piston up thru the exhaust cycle and down thru the intake cycle.
The valves close and the remaining energy in the crankshaft attempts to drive the piston up against the compressing gasses. It barely has enough energy to start the next compression stroke when it runs out of power and things come to a stop with no further movement.
Success. The engine suffers no damage.
Now, on another shut down everything goes the same except this time, during the final attempt to compress the gasses, the crankshaft has quite a bit more energy.
Why? No one knows. Maybe an angel pissed in your helmet.
Anyway, with this extra energy, the crankshaft drives the piston almost to TDC before coming to a stop.
The compressed 100+ psi gasses now trapped in the cylinder promptly shoves the piston back down, driving the crankshaft rotation backwards.
The sprag clutch, which has been sitting idly by while this happens senses the crankshaft moving in the wrong direction and suddenly locks up on the crank.
The energy of the compressed gasses and the newly found energy of the now, backwards rotating crankshaft is suddenly transmitted thru the sprag clutch to the starter drive gears which try to accelerate the starter armature.
The stationary inertia of the armature, coupled with the gear ratio of its drive gears gives the armature a large advantage in its effort to stay motionless.
Suddenly, the brittle hard teeth of the sprag clutch must absorb this large amount of energy.
Maybe they break. Maybe they just begin to fracture.
In any case, the sprags life is materially shortened.
If they didn't fail, they are one step closer to the time they will.
This is the kind of "kick back" that happens.
There is no real outward signs of it except for maybe a "clunk" sound. Maybe no sound at all.
I guess, you does what you does and takes your chances.