What ever kempy puts in his bottles works, I don't measure it I just give a little squirt. On occasions I have put a little to much in ( in my opinion ) but I just connect up and fill the van as am working to dilute it back again.
I think what ever additive is used as long as it's in or about the right amount it will help with cleaning and not leave and residue behind, as it's diluted to the level it is.
Am not sure how many tank fulls I get out of a bottle but at the price it is, it's worth having a bottle for when it's needed.
Some one else may come along in a few weeks and say 1 x 5ml spoon of fairy liquid is perfect dilution rate for 500L tank, of pure and don't leave no residue behind, or Dave will finally crack what's in vision and post it, then we can all buy it for 50p or whatever it is.
What ever additive anyone is using, be it at the correct levels to not leave anything behind definatley helps
I have been using virosol to clean really dirty glass, am finding that the virosol isn't getting it up good enough in certain parts so we have gone back to the supplier and are now using there heavy duty degreaser which is really fantastic. It's giving us the gliding feeling that vision gives and is really cutting into the ground in dirt.
Sometimes it's just a case of finding what works.