That stuff works well for about a month before you begin to smell the cigarette again, but all it's doing is masking the smell. I can assure you that it's not removing any of that old cigarette stink from the seat cushions.
And before you use something like Ozium, be sure to replace your cabin filter. I would say that probably 90% of the people out there aren't even aware that your car has a separate air filter for the interior AC/Heat system. It sits getting gunked up for years, and then you go
through all of the trouble ridding your car of the smell, only to be blasted in the face with stale ashtray the first time you turn the heat on.