Pros: Astounding performance
I've had my share of Etymotics, Westones and Shures, over the years (and with flights and funds increasing) upgrading through their ranges. I've also been upgrading the sources; having rediscovered mobile music (from Walkman days) with an iPad mini, then various Nanos, then phones.
I bought these last year and they made a massive step-change in what I thought was possible in every sonic aspect vs the previous portable gear I'd owned or heard. They even challenged my main stereo in terms of resolution; both disturbing and impressive at once.
Being so capable, they sent me down the source upgrade route - I velcro'd a Vorzugge Pure amp to my FLAC playing iPhone. Then bought an AK100, and strapped that to the 'Pure - and now I have an AK120.
I can bore you with my impression of the sonics etc; but my point with this story is that these earphones produce better results with every improvement in what I feed them. I'm hearing whole things, not details, in music I've had and loved for decades. Yep, they're bloody expensive for earphones, but I believe they are pretty much future proof; sources will get better faster than these will date - and when they're finally overtaken, it'll be a minor miracle - and probably worth the upgrade price!
I've mentioned elsewhere on here how I preferred these as I felt they were more balanced and neutral (I love big extended bass, but not at the expense of overall balance) than another top end unit I tried, but whatever your preference, I can highly recommend splashing a good proportion of your HiFi budget on really good IEMs. These FitEars get a huge endorsement from me of course - but never mind that, go and spend a mildly embarrassing amount of money on the best earphones you can afford - you'll get over the buyer's remorse after a few tracks!