The smell was really bad during the Cleanse Smart 30 day kit. It got better in the 3rd week. I think it helped the liver produce more bile and got rid of a lot of old fecal matter. I was much more regular after that cleanse and fecal odour was gone. Digestive odours remained though and armpit/foot odour. It was a few years later (this summer) that I found the mushroom extract.
I think Champex will work with or without a cleanse, just will take a lot longer without doing a cleanse first. See no reason why you can't do a cleanse at the same time. Most formulas are gentle enough that you can take supplements at same time and Champex is just a supplement, right? Do what seems best for you though.