I remember once last year fishing a river with bread and sweetcorn and only getting a few bites, nothing much. Thought I would try some garlic and chives cheddar cheese for the first time as an experiment. Immediately I caught a big roach followed by several other good fish fish. Tried on other occasions when the fishing was bad and did not always work especially if the fish were really not having anything.
My conclusion was that if the fish really were not feeding, using flavors/additives was not going to make much difference but, if they were just being slow and finicky then something with a flavor/additive could really make a difference. I have noticed similar outcomes with other flavored baits. That they will make a difference on certain occasions and conditions but, not always, especially if the fish are just not feeding full stop.