I dont like answering opinion based questions, but I really like Fahrenheit so...
I use a Fahrenheit in all of my fire decks (mostly) because it adds a serious punch for low cost. Especially in Fire Bolt/Lance and Golem decks, since both of those use very little fire quanta, and focus more of saving it up. So as your fire goes up, so does Fahrenheit's attack, which is a unique feature no other card has. Excluding the Bolt cards, but those are one time uses as Fahrenheit stays until removed by an outside force.
I guess people overlook it or just exclude it altogether to try and make room for a better card to help the deck, but in reality, just adding this card could be the different between a win and a loss.