I have a question about bitter apple in realtion to cats?

i just read an answewr someone gave to a question about cats pee on couches. anyway one of the things they suggested was to spray bitter apple to stop cats from reoffending. i was wondering is this because they dont like the smell? does it smell bad to them? worse, will it smell bad to me? most of those stay of sprays smell like burnt rubber and end up keeping me away and not the cats. why don't these companies make a strong citrus scent stay off spray as cats are supposed to not like the smell of citrus. i think all of my cats have sinus issues as nothing deters them. i could be walking around in a gas mask because of the spray stench and they will be rubbing around the stuff that is supposed to be keeping them away. anyway i like the idea of bitter apple, but i thought it sounded more like a taste issue thing than a smell thing? you know "bitter". i dont want to waste my money if the smellof it wont keep the cats away.