I understand in the OP's situation, being on TRT. In that case, I wouldn't see any problem with it. I still wouldn't see any
problem with running S4 along with test cyp; I just don't see the purpose. For someone not on TRT, I would think saving the S4 for a separate run in between cycles would prove more beneficial. If it were me, I certainly wouldn't run S4 as part of a test cycle. That's what other compounds like EQ or tren are for