Yes, I expect to be holding ZBB for a while too. The more I look at SZYM the more I like it; however the sad shape of the world's economy creates concern that oil price may decline in the short term even as the supply of liquid fuels becomes more dire over a 5 or 10 year perspective. A price decline might make it much harder for this firm to grow or survive.
Currently my plan is to buy an insignificant position to insure it looks me in the face every time I look at my screen. Also have a list of similar firms to review.
Right or wrong, my perspective is that the demand for liquids fueling transportation will run up against supply/price constraints. Life and economies will change and things like SZYM become important.