Cigarette lighters are often used by band teachers for emergency repairs. The disadvantages of these are the metal portion at the top gets hot very quickly and can burn your finger as you are holding the lever down to keep it lit and the flame can leave a black soot on the key.
The beauty of the Blazer butane torch is that you can direct the flame any direction. With the cigarette lighter the flame always goes up so you have to hold the key cup directly above it which can be awkward in many cases. Heating shellac to adjust a pad should just be done to the point that the shellac goes into its "plastic" state. Overheating can turn the shellac to liquid and even make it bubble.
Those who are serious about heating keys and adjusting pads can remove a key from an instrument, remove the pad, clean the key cup, and then melt some shellac (or hot glue) on the inside. When that cools, one begins counting as the heat source is added to the opposite side. This way makes it is easy to see how many counts it takes that particular glue to go to its plastic state, liquid state, and get the fire extinguisher state (which is just past the "boil, boil, toil, and trouble" state). As one becomes familiar with the melting properties of the glues used to install pads, the process becomes more intuitive and less fraught with mistakes and burned body parts.