Comma Air Con Cleaner
I thought I'd share my experience of this stuff, which I recently purchased from eBay.
I've been sneezing a lot recently and I suspect it's because my cars air con has some bacteria in it, so I got hold of some Comma Air Con Cleaner.
It has certainly made the car smell fresher. I have just run it through the system having changed the pollen filter a few days ago.
Unfortunately the button on top is badly designed and "locks" in place too high up to engage the spray.
I ended up wedging a flat head screwdriver over the button and taping it down, then blue tacking the end of the screwdriver against the front of the seat to stop it falling over.
Doing some research it seems I'm not the only person who has had this issue, so my advice would be to buy another brand if you want to run some cleaner through your air con.
I did buy two and the other one is the same.