Quality of optimizor heads

I bought my twisp edge at the forest hill mall, after coming from the twisp solo which disappointed. I bought the tabacco flavor at forest hill which tasted great but when I bought optimizor heads in rustenburg the taste changed abit but was bearable. I then bought optimizor heads from middleburg during the festive the taste then changed into something else which I had to bear because of the remote location of my holiday destination. Yesterday I went to the Brooklyn store to purchase the liquid and optimizor head and I was informed that the heads I was using are old and of an inferior nature, even the one I had installed the night. Now with the latest optimizor heads the taste has once more changed to a choci taste although I am using the same liquid, tabacco. I'm lost now.