This is my first write-up, and my impressions mirror a lot of what's been said, but here goes nothing -
note: I am currently at about 30 hours of burn-in, alternating between Laptop's headphone-out and USB DAC to Headstage Arrow 3G.
Snatched a pair of these only after hearing about the Newegg $150 plus $50 gift card combo deal, as I've been completely smitten by the JVC FX700s, which I've owned for a year and a half. Straight out of the finger-hating plastic container, I got a really good fit out of the smallest-size tips (weird, as I've never liked bi-flanges in the past).
No serious complaints about the build quality or construction, though the cord is a bit on the stiff side,
and it would be easy to confuse the left and right pieces in the dark. (Corrected, thanks James!) Probably obvious, but they are incredibly tiny!
Similar to what tienbasse
stated, the EPH-100 seems to have its strengths where the JVCs aren't at their best. The Yamahas were on-point when listening to rock music (intentionally-vague here). The JVCs were left sounding a bit congested and ill-suited in some situations - a credit to the Yamaha's wider soundstage and instrument separation. At the same time, the JVCs remain (at least in my ears) king of EDM. The Yamahas certainly don't lack for bass presence, but they don't quite match the punch that the JVCs deliver. The main difference is in the highs, where the Yamahas can sound a bit flat compared to the stunning show the JVCs put on.
While the Yamahas aren't as easy to drive as my Super Fi.5 Pros (RIP), they are on-par with the JVCs in that regard.
The biggest impression came from when I took the Yamahas off and returned to my JVCs after a couple of hours: Something akin to stepping out of a limousine and straight into a vat of acid - The JVC's sound was super-fatiguing comparison. While it could be due to my ears adjusting to the change in fit (far deeper insertion for the Yamahas), it was certainly jarring. More swapping later on proved to be a lot less traumatizing, but in any case the EPH-100 is a keeper, and with the incredible deal I got, a steal.