i've used Oxypowder before. i think it's good for emergencies, but not so much as a bowel cleanser. i noticed that if i drank a lot more water i would get a lot more butt pee, but not much regular urine. it felt pretty good though. it cleaned me out fairly well, but toward the end of the dose, which is usually after 16-18 hrs, eat very lightly or else you'll feel clogged up and have to wait for your bowels to readjust. takes a few days before you get the urge to use the bathroom.
i've never used colonix so i don't have anything to say about that. best of luck