Here is how I can see some of them working if you had an itchy scalp. You rub them on, you scratch less, less telogen hairs fall out, and for a while, as long you didn't rub too hard, it looks like it's working.
Or, you rub it on, right before a bad, but natural shed, and then the hair grows back. Voila! It's working, until your next big shed, that is.....