Gatsby, I am still using the 13.5, however, I have noticed that my Zap is running warmer than it did when I got it. I also notice that by the end of a session with the 13.5, or if I leave it plugged in for a while, the 13.5 makes the Zap run hotter than I want it. I think this means I am close to the end of my "break in." Personally, I think for the small dollar amount the 13.5 costs ($10 shipped w/unit, $15 shipped separately) is worth it. Even with the extra adaptor, it places this unit, cost wise, under the cost of the other log vapes.