This is the most useful weapon HANDS DOWN. its heavy sure. But being able to melt the amour off of those amoured charger zombies is worth the space in your backpack. But to be honest if you find a flare gun and upgrade it with weapon parts theres not much of a reason to craft the flame thrower anymore. Unless you ran out of flares that is. But you probably wont run out of flares if you save the flares for just the amoured chargers and nothing else.

Later on you can pick up 1 scrap, 1 gear, and 1 oil filter right from Hector at the starting point and craft a flamethrower before beginning the run.