Not bad! It is supposed to have 0.5 watt of audio power and the speaker sounds quite reasonable.
As a test, on the FM broadcast band playing music, I cranked it up and it sounds like a good pocket radio. But it's not hi-fi by any stretch. I'm just trying to convey that it's not bad.
As far as I know, the FM Broadcast band is mono only. There's no sign of stereo output and no mention of 'stereo' anywhere.