As far as I know, there’s absolutely no basis in fact for the whole ‘putrefying toxic matter in the colon’ thing that always gets used to try to sell these types of thing.
It’s an easy sell and an easy leap to make, because that’s where poop comes from, therefore it must be icky - but our intuition and assumptions often let us down in the absence of evidence.
As someone who used to suffer from Ulcerative Colitis, I’ve had several colonoscopies over the years, so I’ve seen the inside of my colon plenty of times: you stop eating for 24 hours and it’s empty - just a pink tube.
Your colon has a very similar structure to the rest of your epithelium - your mouth, your throat, your stomach - that whole tube that runs through you. Like the rest of it, the colon is a flexible tube of epithelial tissue, lined with specialist cells, kept moist and lubricated. It’s no different than the rest of the system, really, except by degrees - we just think it’s like an icky sewer because that’s where we send the end product.
Toxic waste products don’t build up in your throat, so why would they in your colon? By definition, the rate of throughput at one end is about the same as at the other and, unless you’re constipated, things don’t hang around in your colon any more than they do in your stomach.
This ‘kit’ is just a laxative, fibre and a pro-biotic, so I doesn’t seem like it would do any active harm - but probably not a great deal of anything else either.