most people get exceptional results, however not everyone for various reasons.
some smokers or former heavy smokers do not respond, though some do- but smoking or former smoking can be an issue.
some low carbers find that they have to increase carbs to see the "strong" effects.
for some people its too strong (hence the 1 cap warning)
for some people, like the 2 people who were former methamphetamine addicts, found it to not do much for them... though given the posts they made, not much worked for them.
diet and water intake can play a big role in response, not always but for some people they need a higher carb/water intake to get the "great" results.
then as with anything there are some, very very few, people that dont respond for any known reason. Like the way that some people can take a gram of test and not make gains (yes its actually possible)
though as stated above generally the response and results, particularly the positive impact on cardio training, are exceptional.