JayBird doesn't stop there. The box also contains a set of detachable earclips and seven sets of eartips in a variety of sizes and textures, including one double-flanged set and one triple-flanged (to accommodate those with deeper ears). Both items are to ensure that everyone gets the most secure fit possible--an important consideration for any "athletic" earphone. However, it's important to note that the earpieces themselves are rather bulbous and large, so although they are shaped with the ear in mind, they may not fit everyone comfortably. If you do get a good fit, though, these 'phones provide a fair amount of sound isolation, so outdoor runners take heed: these are better suited to the gym.
Another important consideration, of course, is sound quality, and the JayBird Endorphin Rush earphones seem to be up to the task overall. We did notice that certain songs had a tendency to sound hollow and were lacking in warmth, but this was not a persistent problem--at least not enough to subtract any major points. The highs were also not as tinkly as we like and had a tendency to roll off, but not so much that we wouldn't recommend this set for $99. The real standout here is the bass, which is superthumpy and encompassing. The deepness of the low-end is truly stunning for earphones of this size. Hip-hop and electronica were real stars in testing, but it wouldn't be a stretch for a multigenre listener to like the Endorphins. Certainly, another plus for some people will be that these earbuds require very little power to drive, meaning your headphone amp can run lower (we listened to music roughly 10-percent lower with these than with the Klipsch Image S4).
In the final analysis, the JayBird Endorphin Rush earphones are a solid buy in the $100 price range, particularly for active folks, thanks to their supersecure fit. (Yet they are not the best option for street runners and walkers, because of the sound isolation.) Bass-addicts will also be extremely pleased by the amount of oomph offered.