I ordered this yesterday and it has just arrived.
What they don't tell you what I didn't read on the website is that it is professional strength and to make up a solution, you only need 100ml to make up 1 litre. So cost of 1 litre ready to use = 64p compared to simple solution 945ml about £5.99 - and this is supposed to be much stronger as well.
The only snag is I thought it was ready to use strength so I bought a 5L and a 500ml spray bottle to refill so I will need to empty it into another container. I think I have an empty bottle from another brand.
The proof of the pudding as they say so I will try it later. It also contains an airicide. I am very hopeful considering some of the products they sell are for hospitals, morgues etc
55 Litres should keep me going for a couple of weeks with Willow
http://www.xeria.co.uk/kolist45/1/Full%20Product%20List/26/RX66J.htm