I'm guessing that if you drink cocoa instead of taking cocoa flavenol pills, the sugar and other ingredients probably negate the effect.
I use coconut cream, instead of bulletproof-style coconut oil, because I need my morning coffee to be somewhat palatable.
On the other hand, as pointed out by the study, these are flavanol supplements purchased from Amazon (Mars/CocoaVia brand). A quick look at US Amazon shows this being quite expensive though (IMO).