I've used similar products with ground psyllium and fenugreek seeds. Be sure to drink PLENTY of water. They say the stuff can turn to near concrete othewise.
I worked at the San Diego branch of the Optimum Health Institute in '88.
http://www.optimumhealth.org/
Have been a guest before and after. They do raw foods diet with wheat grass juice and a 3 day fast the first week, not technically a complete fast because you have raw vegetable juice and wheat grass with it.
Part of the process is daily enemas followed with a wheat grass juice enema. Does have quite an effect. I saw people come in looking pasty and listless and after 3 weeks, they'd be rosy cheeked and more lively. One week stay minimum. Reasonable rates. They have a place in Austin now, too.
I think this method, specially with a colonic added, is better than the intestinal cleansing powders, but it takes longer.