Really amazing sound quality. Clean sound, bass is softer and less impact than ZX300, but pretty deep, good body. midrange is neutral smooth but detail is enough, treble is good energy, not too shine, not too dull. FA3S can compares with Chinese DAPs around 350$ i've tried like Ibasso DX120(Much better), Cayin N5iis or even ZX300A. But firmware is not stable, fast but not a intuitive UI, crash. Battery is good also, about the same as ZX300. Heat is not a concern when music played, if you turn machine on but dont play anything heat raised fast(Because of class A amplifier) . 13x$ is bargain in term of sound quality