Andrian, beside Ben and the New Jersey Hirailers, other have replaced their REV Ls with older versions and been OK as long as fast breakers are in place. I don't have a lot of derailments but enough along with broken shorted equipment to test the TIU. My layout is also my test track and many items come to me for repair have short circuits.
BTW when I had the cover off my TIU I noticed it has a number of 20 amp automotive fast blow fuses. I assume MTH must think their TIU should handle up to that so a 10 amp fast breaker should be more than adequate.
RJR, how much do you think someone else would have to charge to design sell at a profit another fast breaker. I suspect it would be more than 50 bucks which is what the others sell for now.
Pete