It uses enzymes to break down the bacteria causing the odour rather than 'masking' it, not for my car of course, but for her indoors' Astra which the kids get ferried about in, gets eaten in
and gets to do the runs down to the tip 
Comes in a 1ltr bottle and dilutes @ 5:1 (costs around £8.00) it's also handy around the house on carpets, mats and even shoes.
Works best when kept damp so if you've sprayed a patch then put a damp clean cloth over it for 12 hours to keep the action going.
