Hey bro, I dont know what it is about that blend but that ester just hurts me in anything but Test Cyp...I have used many Cyp products like Syds Nandrolone Cyp and had the worst pain ever....Cyp and Undec are not that far apart in esters bro, the end results will be almost identical...Remember the ester does NOTHING to change the drug, only changes the speed in which it is released....