I hardly think those 3 posters had "an agenda" to sell you their ashwagandha, since only one of them mentioned a brand, and then only when asked. As it's a natural substance, it won't be patentable and so no-one is going to make a fortune out of it. I think they were trying to be helpful.
I have a small packet of powdered ashwagandha for adding to food, which cost me the princely sum of £3.64 in a local health food shop.
I got it after reading up on ayurveda, and it was the top-rated superfood of all the ayurvedic herbs/spices for many health reasons.
I haven't tried it on a dementia sufferer as my knowledge of it came too late to help my Mum. But I add it to my own food from time to time. I find it energising in a general way.
Here is some more info about it, plus more general advice about improving your brain health -
http://articles.mercola.com/sites/a.../ashwaganda-effect-on-alzheimers-disease.aspx
I doubt if western doctors have heard of it and they are most likely going to play safe and tell you to take nothing but their own products. But some side-effects are mentioned here:
http://www.webmd.com/vitamins-suppl...-953-ashwagandha.aspx?activeingredientid=953&
The "side-effects" could in some patients be beneficial, like boosting your immune system and raising thyroid hormone levels.
The user reviews are worth a read, as they are very mixed (obviously not all talking about the same specific supplement).
It would be sensible to try out any ashwagandha supplements on a non dementia sufferer before giving it to them.