What chain is Harmony One on?

Excuse me, could you please elaborate on the underlying blockchain technology that Harmony One is based on? I'm curious to know if it utilizes a traditional proof-of-work consensus mechanism or if it has opted for a more sustainable solution like proof-of-stake. Additionally, how does Harmony One's chain compare to other major blockchains in terms of scalability, transaction speed, and energy efficiency? Your insights would be greatly appreciated as I'm considering investing in this project.