Hi,
I used this brand of henna once, I believe in medium brown. I liked it fine. I have natural highlights that are the same color as well, and it turned my hair reddish. Definitely darker, not lighter.
My only problem with it is that it was soooo hard to wash out because it is not well sifted. There were twigs, etc in it. It took forever, so I've moved onto finer sifts.
I'd say it definitely worked though. My hair felt stronger (not softer though, but that's a side effect that can occur for all brands of henna, and may be my error more than the brand of henna).
I think that the colors are different because of the indigo content. In the box were two packets that I had to put on separately. I believe the first one was straight henna, and the other was indigo. I'm not quire sure though, how they get degrees of color. Maybe percentages of indigo/cassia? But I'm not sure.
Hope that helps!