The 20,000 TBC Flamethrowers sold out quickly for $500 each.
That's around 40 times the original $500 (£374) price tag.
The firm plans to build a network of tunnels where vehicles are transported on electric skates to their destination, reducing traffic on the surface.
Elon Musk's tunnel startup The Boring Company began distributing its first 1,000 personal flamethrowers to buyers over the weekend in Southern California.More news: Everything that happened at Ubisoft's Aisha Tyler-less E3 press conference
Musk tweeted photographs of excited fans shooting flames from their new toy.
As the promotional device started to land with customers, Musk posted a safety warning to customers on Twitter, stating: 'Please use as directed to avoid unintentionally burning things down.
It continued: "I will not use this in a house, I will not point this at my spouse, I will not use this in an unsafe way, The best use is créme brulee".
Earlier this year the word came down that Elon Music and his Boring Company had pre-sold more than 20,000 flamethrowers. Despite the fact that Elon Musk's flamethrowers are clearly not guns, they fervently objected to Miguel's bill, which was finally quashed, with Santiago noting that "Our bill right now is in the appropriations committee in the suspends file". Instead, they work more like large propane blowtorches.More news: Trump arrives late to G7, reschedules Macron meeting
The device comes with a 10-page manual which had additional tips: "Do not touch the not-a-flamethrower nozzle during or after use, as it could burn you".
Another part of the agreement absolving Musk's company from liabilities from customers' behavior "no matter how genius or stupid" included exemptions for such acts as "setting things on fire", and "smoking near the not-a-flamethrower". The funds made through these "hot" sales would be, in turn, used to fund other ventures of The Boring Company.More news: Anthony Bourdain's mother says his body is stuck in France