There are a number of vaporizers currently on the market but they have only two mechanisms of use. They can either work via conduction or convection. Machines that use conduction transmit heat through the herb by allowing it to touch the heating implement. Then there are convection machines where the heat is transmitted to the herb indirectly through the air.
Vaporizers that utilize conduction are not the best option because on the portion of the herb that is touching the heated implement will be heated properly enough. This means that these machines cause a large amount of your herb to be wasted and doesn’t provide the most effective delivery. One may try to increase the temperature to get more from their machines but that may only cause the herbs to overheat to the point of combustion which defeats the purpose of using the vaporizer in the first place.
You will find conduction vaporizers referred to as soldering iron vaporizers very often. This is because most of these use a soldering iron element along with a bowl where the herb is placed on top. If you have a vaporizer that looks like a jar with a heated stick inside then you more than likely have a conduction vaporizer.
Vaporizers that use convection are better options since they do not directly heat the herb with a heating implement. In these devices the herb is heated equally thus providing better vaporization
Convection vaporizers are much better because heated air can flow all the way around all parts of the herb. This ensures equal heating, and consequently more complete vaporization. As long as hot air flows through the herb and there are essential oils left to vaporize, it will continue giving off vapor. These have their cons though since there are a lot of variable that affect the heat of the air that flows over the herb.
The latter are the more expensive choice because they you a thermostat to control them. Since there are so many variables that affect the heat of the air in these devices extra care must be taken to ensure that the heat is heated equally and kept at a constant temperature once it gets there.
You will find that some vaporizers seem to use radiant heat but in fact they use mostly convection. Radiant heat is hard to control and would require measuring the herbs surface temperature and this would require the use of IR thermometry which is very expensive.