I would recommend Oxypowder to you, because Oxypowder works great for those suffering from constiption. Mainly because it's really easy to pass the fecal matter. With Colonix, the herbs 'bulk up' inside of you, and sometimes it can be difficult to pass during a bowel movement, because you have to strain to get out the psyllium-rope.
Although, both products are good. Both companies are known as respectable & reputable companies. I don't think you would go wrong with either product.
But for me and my body, I reacted better to the Oxypowder .