Completely burning butane produces essentially only carbon dioxide and water vapor, which are harmless. Other compounds are created in trace amounts (partially combusted hydrocarbons, NOx, etc). Lighter exhaust is invisible, which is an indication that it contains little soot. Butane lighters burn quite clean, provided that the flame is undisturbed (i.e. not flickering or touching the filter). A flickering flame, or a flame that is touching the sides of the intake will produce undesirable unburned hydrocarbons. Consequently, technique affects the cleanliness of the vapor. However, even sloppy use of the VaporGenie will not produce nearly as much toxic material as found in smoke. Lighter exhaust is a LOT cleaner than a regular pipe, and that is very apparent once you try the VaporGenie.
There will necessarily be some toxic material in the lighter exhaust, however. We believe that more toxins and weird chemicals are released from the plant matter being vaporized (compared to the lighter exhaust), especially if it is overheated. Even in electric vaporizers, there is some tar and toxic chemical production. It is impossible to completely eliminate exposure.
Always remember that you get the cleanest vapor when the flame is not disturbed, flickering or touching anything. You don't want the flame to flicker or touch the filter or sides of the pipe.
We have found that some people (perhaps 10-15%) appear to be especially sensitive to butane lighter exhaust. For these people, we strongly recommend the Ital Hempwick lighter, which we sell (see the lighters products page). The Ital Hampwick is made of organic hemp twine saturated with beeswax. The exhaust from the Ital Hempwick has a pleasant beeswax flavor.