A recent review of all the medical studies into colonic irrigation showed little or no evidential medical benefit, but a fair bit of data suggesting quite a range of side effects, from minor to pretty serious.
Personally, I can imagine it would lighten your wallet but do little else of benefit, and I can think of better ways of spending my money.
A couple of links for you - even one from the Daily Mail, which usually embraces alternative and complementary practice with gleeful abandon! :)
http://www.dailymail....just-money-drain.html
And one more scientific link, from a very recent review of the medical literature.
http://explore.george...19&PageTemplateID=295