Stepped transmission design has been well understood for a long time and things have been pretty straight forward with few problems now. CVT seems to be still a bit of problems in the mod scene and I have seen Civic CVT slip if someone chipped their engine and floor it in street racing (stupid I know, but it is indeed a stress test). I haven't seen people slip their stepped automatic transmission street racing a modded engine so far on the road. This means there is not as much safety margin on CVT for fluid spec to make mistake on.
It really boils down to do you trust the aftermarket brand testing everything to like OEM, and whether you are going to drive it with corner cases (extreme temperature, extreme torque, extreme deceleration, forgetting to change the fluid once, etc).