The harvester is such a fun weapon for Pyro in TF2 Classic. Really good for playing a chaos pyro. Just run in and light everyone on fire then when you get spotted switch to it and absorb damage as you escape. Then you’ll have a guaranteed critical melee attack for later.
And while this strategy is fun it does come with risk. If you die everyone you set on fire instantly goes out. They have a big incentive to outpace your healing and if they do it was pretty much for nothing. Cool weapon.