The title BETS salt is a quasi-two-dimensional paramagnetic metal with a high-spin localized at the Fe^III site in the tetrahedral anion FeCl₄. At T_MI=8.3K, however, it undergoes a metal-to-insulator transition spontaneously associated by antiferromagnetic (AFM) and ferroelectric-like orders, and also by the structural transition. An application of a high magnetic field makes this insulator unstable against reentering the metallic state, followed at higher fields by a transition to the superconducting state. These unique properties totally indicate noticeable spin- and charge-correlation of electrons in the crystal lattice with localized d-spins. This article reviews these phenomena focusing on the AFM insulating states and high-temperature metallic states exhibiting a multifunctional interplay among the conductivity, magnetism and dielectricity. Discussions will be made on the anomalous metallic state, in comparison with the isostructural, superconductor GaCl₄ salt exhibiting contrasting anomalies in the metallic state.