I recently used Lush's Henna bar in Caca Noir. At first, I did not notice a big difference in the tightness of my texture. By the time my hair dried I did see a slight change. But, it's not what everyone makes it out to be. My ends curled much more and my hair did clump more. But, I was still a 4b, with more definition.
In my honest opinion, henna is a wonderful conditioning agent but I don't think it loosens hair texture. It's more of a "hair revitalizer" to me, meaning it will restore my hair to the texture I was genetically designed to have in the first place. But, I cannot see my hair going from 4b to 3c or 3b with consistent use.