I played around with them, borrowing one from a friend.
They definitely have their use case, the most obviously being when you need to keep your ears open for traffic or whatever.
However, I felt that the sound definition was not great, especially for sharp sounds like cymbals. Everything felt a little muffled, and it couldn't hit highs or lows very well.
It's one of those "better than nothing" pieces of tech but not what I'd choose for pure listening enjoyment.