The Pro Piezo or the Pro II?

How short on the fuel? I rarely need to do something that would require more than 15 minutes or so of work.

The thing is that I bought a RadioShack branded Professional a while back and it never seems to be hot enough. Or rather, it's hot enough until whatever I'm soldering wicks all the heat away from it. Maybe it's defective. Or maybe I just don't know how to solder....
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Bitt Faulk