Unfortunately I am sure that I must have shares in DAP by now!
I have a large open plan kitchen/living/dining room so I would need about 3 or 4 diffusers going at once to have any effect, and at £15 a refill, maybe not!
They had NO effect on Sophie whatsoever anyway - even after using them for about 3mths.
I use the DAP spray on the bedding in the crate, and it did seem to work with Sophie for a while, but as with everything else, only lasted for a while then it was useless. At £17 a bottle, it is quite costly too, but seems to last a lot longer as you are only using it when you go out and not all the time.
Sophie was also on Skullcap & Valerian tablets for about a month, but they did nothing either. She also had Bach rescue remedy in her crate drinking water - so now you can get the idea as to how worked up she was getting - all those so called "remedies" and she was still a nervous wreck when I went out!
Beau, being in the same crate as Sophie, was also getting the benefit of the DAP spray, and I have just continued that with him on his own - but it clearly had no effect on him today whatsoever!