Pros - Mid-focus, decent bass for single BA, smooth treble.
Cons - Congestion-prone. Sensitive/hissy.
A mids-focused specialist with a little bass thump and smooth, relaxed treble (recessed, but still has some detail).
Not an especially engaging sound (a little too relaxed maybe).
Decent across genres, but tend to congestion during busy/noisy passages.
I find them particularly useful for low volume podcast legibility, though with podcasts that are poorly leveled, subject to intrusive volume swings.
Possibly showing their age a bit, and there seems to be a lot of competition in the under-$100 of late, including Zero Audio's own follow-ups.
Carbo Tenore and Doppio I more readily recommend, but I think BX500 still have appeal/utility given their focused signature.