The increasing use of stronger motors has shown that the hollow main rotor shaft of the TDR is in rare cases earlier reaching (but not exceeding) the mechanical limit.
Furthermore it react very sensitive to loosened or not tightened enough main rotor central screw.
The hollow shaft is also very sensitive towards short hard knocks.
Minor accidents like overturning during a bad autorotation or any other ground contact of the blade can generate little invisible cracks, which might lead to a higher risk of a broken shaft after some time.
Safety is our prime concern, so I only distribute the more durable full shafts. They weigh a bit more, but are less sensitive to accidents and are more safety in marginal burdens.
Again, the traditional shafts are safe as long as they have not been damaged in accidents. Still, I strongly recommend to change over to one of the new full shafts. Better safe than sorry.