Actually provided people first understand what essential oils they are using, sourcing etc. they are generally safe even with coffee.
This business used a series. First water/soap or just water, second oils with distilled water, third coffee, I would think that the oils are still attached to/infused into the colon tissue when the coffee comes in (last part of the series).
I agree that one has to be safe and know what they are using, however, the fact it is self healing here one hopes most would look around and not take the advice of just one or two posts.