TL:DR: power output is inaccurate by a significant margin compare to a trainer.
I have seen several threads in this forum related to the power output of the IC4. Instead of replying to each of those I just rather create a new post with my findings. I initially bought an IC4 to introduce myself to Zwift and cycling in general but after getting so quickly to A cat I decided to buy a Kickr Core trainer and the number could not be more different. Data:
FTP test with IC4: 350
FTP kick core: 217.
In my races I was averaging over 330 with the IC4 now I can barely get to 200 Watts. In turn I moved from an A racer to a middle pack C (no regrets).