I had the misfortune recently to follow someone to the disposal point who had not flushed and had left an almighty stench. I assumed they were not using any fluid at all but perhaps they were washing liquid users. Very bad idea in my opinion, we hear of tales of novovirus rampaging through cruise ships, it will be caravan sites next if this idea catches on.
And while we are on the subject I would be cautious of buying little known brands on e-bay ( I'm not referring to Blue Diamond here, I have seen that for sale in reputable outlets). As far as I can see there is no standard that these fluids have to attain, anyone can just put a capful of disinfectant and some blue colouring into a bottle of water and call it toilet fluid.