re: beetroot juice (& dark chocolate)
Due to recent revelations, I’ve done a 
load of reading on this stuff.
As @Pete says, you gotta take a TON to reap the benefits. And yup, it’s nasty.
However, the nitric oxide in the BRJ isn’t super robust and one of the best things to mix it with is pomegranate juice which preserves the NO efficacy. My ratio is 3:1 BRJ/pom.
I’ve been downing 500ml of BRJ/day for nearly 2 weeks (for health reasons, not performance).
My resting blood pressure has dropped 5% and my exercise-induced hypertension BP has dropped 30%.
(I now have the BP of a child and an old fat lazy smoker.)
The reason caffeine (and chocolate) negates the BRJ effects is because caffeine constricts the blood pathways and NO dilates those same pathways.
As for dark chocolate…same deal…you gotta chow down a lot of it to get material benefits. Probably better ways to get better results.
Bottom’s up!