Flamethrowers were weapons capable of firing concentrated bursts of fire. All sides in the Clone Wars would utilize them in battle. In terms of technology the flamethrower was rather primitive in theory. The user would fire at close range using the fuel from a pack, this fuel, in turn, would be ignited by a current of energy producing a jet of super hot flame.
Although these weapons could be devastating on a battlefield and would be relatively easy to produce flamethrowers saw little use in the Clone Wars. This is likely due to the inherent dangers of the weapon, for example if a soldier wielding such a unit was fired upon by an enemy a single stray shot could potential pierce the flame unit's fuel container and ignite all the fuel resulting in a massive explosion. This explosion could take out not only the flametrooper but the entire group of soldiers around them. The advantage of such a weapon is in dealing with enemies at close quarter combat range simultaneously.
On Geonosis, for example, flamethrowers were very useful in engaging the Geonosian defenders in the underground catacombs where they had dug in to face Republic soldiers. The enclosed nature of these caves meant that space was limited, an entire group soldiers were packed together and thus could be incinerated all at once by a flamethrower. The weapons could be miniaturized, and many Mandalorians, such as Jango Fett and Pre Vizsla, used them on their gauntlets.