Probably not particularly necessary for healthy individuals, but could reduce the amount of work needed to synthesize your own transmitters (few steps rather than 'from scratch'). Perhaps some individuals with neurotransmitter deficits could see benefit.
As I'm sure you can tell though, I'm not a trained neuroscientist.
That makes some sense. By itself, I can't think of how it would benefit a healthy person. I'm not even sure what kinds of unhealthy people that might help.
So, to me it looked like, 'Hey, here are some fancy words! Don't look too deep, because they are mostly meaningless.' No offense intended, that's just what it looked like to a curious layman.
I have a commercial wild blueberry operation so I hear some really, really strange claims. Things like this peg my skepticism meter. No, my blueberries won't turn you into Superman or Einstein. They don't cure cancer, prevent HIV, or give you psychic powers.
Nettles have serotonin, histamine, and acetylcholine. Serotonin could benefit certain mood disorders, and acetylcholine supplementation can reduce certain kinds of headaches.
As with all natural foods/medicines, I think you'd typically see only minor benefits over long-term supplementation. Much less powerful than modern medicine, but perhaps fewer side effects when taken properly.
You're right to be skeptical though, lots of snake-oil salesmen in the natural food space making dubious claims. Blueberries are probably much healthier for you than eating Cheetos, but probably not that different from other berries. I appreciate scientists studying which species have the most nutrition, but variance in freshness and growing conditions are probably the biggest factors in nutritional density. ex. fresh raspberry are probably better than old poorly grown blueberries.
Blueberries contain antioxidants! LOL