I ve used for the past 20 runs TIR's front spool with the derlin outdrives, the so called "PRO COMPETITION SPOOL"
I use the stock HOT BODIES lightweight aluminum outdrives which are also supposed to be fragile.
I run on a very large, high speed, medium traction track.
I 've had great success and not a single failure.
To my understanding, running a spool, even one made of steel, is not recomended for high bite/traction, carpet tracks.
As also seen at the ICC LAS VEGAS race a diff upfront is the better choice.
Spools cannot absorb the energy generated from cornering and accelerating as there is no moving part to give way. In this respect when traction is high, it is normal to have problems with durability.
Manufacturers are trying to built them as light as possible to enhance performance, not to make them bullet proof.
I think TIR's spool is as good as they can get. Just stay away from crashes and don't use it on high bite carpet tracks.