[jome]

Well, someone smarter will propably answer better, but my first instinct is to say that being a strong vasodilator, NO would only hurt freediving performances by countering one of the biggest benefits of the dive response (vasoconstriction of the extremities and thus also bloodshift and bradycardia).

Plus being a strong free radical, I'd not be too keen to consume it in large quantities.

But as we know, things are not always not that straight forward and simple. Things that may at first seem to do something fairly simple for the body, may trigger the body to adapt or counter that change in some other way no one has even thought of and cause even the complete opposite effect in long term. That is why I prefer to leave the science and research to those qualified and equipped to do it.