Pros: Very smooth highs and midrange. Nice detail.
Cons: Fit is tricky.Sound is so dependant on fit. Hard to insert. Even the smallest tips may seem too large.
I have both the HAFXC80 and HAFXC51. The FXC51 seems easier to insert due to its shape, while the FXC80 seems to have a bit more detail and be a bit more dynamic. I bought the FXC51 first, and didn't realize when I bought it that the FXC80 was only $13 more. I bought the FXC51 based on recommendations here. These IEMs use a micro driver which penetrates much further into the ear canal than the driver of a typical IEM. This makes the highs much better, as there is less reflection of the sound. It also leads to comfort issues, as the very hard driver enclosure is going deep into the ear. It also seems like different replacement tips won't be so easy to...(read more)