Pros: Seems to have an actual slight effect on cats,
Cons: The smell from the spray, price, doesn't work for what we needed it for
I bought Feliway spray in November 2014 in preparation for a cross provincial move. We acclimated our two cats to it immediately after bringing it home by spraying it on luggage, boxes and the cat carrier. They seemed slightly calm and content about that but then on moving day, they were just too stressed out. First we spent the night at my sister's house (she has 2 cats) so the Feliway seemed to work when we sprayed it on the door separating the cats. Then we went to the airport and no amount of Feliway could have calmed them down. They were in cargo in the plane and then we drove straight to their new apartment - though our stuff had not arrived. Feliway did not help in the week adjusting to this new place.
Feliway does not work when we spray a blanket and put it in carrier for a trip to the vets now. It seems the awful plane ride is associated with this product and it seemingly has no effect any more. Now we just have a half full can of Feliway. There is also a smell right when you spray it which is slightly stingy on the nose, the instructions recommend using the product 20 minutes before stressful event. So I don't see how this would be effective when trying to stop scratching or destructive behaviours.
I recommend people try this product, it didn't do what we wanted it to so we're disappointed in it but we also consider that we put our cats through the most terrifying events of their lives. It was an expensive experiment. Just know it might not work depending on the cat and reason for using it.