After looking a bunch of them over online last night, I'd have to say "scams". As non-pharma, they all contain common ingredients which--like caffeine--are know to increase, minimally, alertness, concentration. But most of the sites "cite" bogus trials or studies or endorsements. Lots are the old, "Free trial amount, then we sneakily bill you each month for a big amount of moola, until you talk to a rude person and get the "agreement" cancelled. Not to say some might not do something. Reminds me of an old joke my mom told me 60 years ago.
A guy showed up in town selling "smart" pills. A farmer shelled out the money, took a few of the pills, and said, "Why, these are just rabbit droppings!"
"See", said the salesman, "you're getting smarter already".
SheratonGibson