A good question.Is there a lot of negative to this model? Why? They are not suitable for smortfonam. Of all the company's headphones fault, these are the best. The sound is good. There were headphones kz 10pro. Thick bass and treble smooth.(google tr.)
ASF & ASX has been received as a quite "mixed bag" KZs, indeed.
In my limited opinion, their really narrow nozzles do not work universally for everyone - different tastes and preferences (or ear cavity coupling).
In ASX, at least one sound guide fires directly into the rim of the nozzle, so it limits/striangulates the sound.
Perhaps, a good acoustic design was just forced into their recent most popular form factor from wireless (?)
Then many enjoy ASX & ASF as far as I know - tastes (and ear cavities) are differerent.
For me, ASX are my favourite pair by far, though with the wide nozzles (from ZSN/A10).
The modified ASX are my most bass-head pair (way more than AST that is touted as bass heavy), rich in mids and not slacking in treble either. They do sound rich and edgy.
As much as I like AST (and give KZ all the due credit for the great BA array and making AST sound most "un-KZ"), ASX wins for my sound preference. Late Beethoven string quartets by Takács are so engaging with ASX, while with AST, they sound just smooth, as possibly preferred by most audiophiles
Then ASF are the only all-BA pair of KZ and CCA that I do not own since I just got a second pair of ASX.