The f111 is a beautiful IEM. Even with it's "typical" fit, the kind of fit you would normally use with this type of earphone, they sound great. They are warmer and less crisp than the etymotic er4s that is its cousin (they use the same driver). However, with a very shallow fit, properly sealed, they take on an extremely similar frequency response to the er4s, while improving upon the imaging and soundstage. The fit is absolutely critical though, and unfortunately, it isn't easy to consistently achieve. I think most people will find these to be warmer earphones, because they never achieve the critical fit described. You'll know when you get it if you are familiar with the er4s, because it will sound strikingly similar in response.
These are comfortable, well constructed and durable. The cable is very nice and tangle resistant, however I can't speak for the longevity of the cable. It isn't super touch, but it's not really fragile either. The connecter is removable and seems very well made. It has a sort of phone connector style to it, like a super mini rj45 connecter without a tab to press (it just pushes in firmly). The ears are easily identifiable by colors and a bump on the right ear (i love this). They are overall a very nice package. The sound is most important to me, and in this regard they succeed highly with either fit. However, with the critical fit mentioned they are very reference quality with er4s like frequency response and amazing instrument separation and clarity. The instruments are very distinct and lively, while being more laid back at the same time than the er4s.
I would say the er4s and f111 are the two best earphones I've heard for reference flatness. If you like the er4s you may not need to try these, especially if you don't want to deal with the fit issues. I'm not sure if these were designed to achieve er4s response, in which they failed with the fit in my opinion, or if they are designed to be warmer, in which it's unfortunate they didn't aim for er4s response. Either way, the er4s improve on fit consistency, isolation and durability (as far as it seems). The f111 improves in comfort, driving sensitivity (easier to power loudly) and 3d-ness.
I highly recommend both. I would absolutely own these if they weren't so pricey while also being difficult to fit perfectly for the best response. They are also hard to find and might be going out of production according to the company that sells them now. So, that's my word on the matter. Hope it helps