Pros: Overall audio quality, excellent value
Cons: May be bass-limited for some, slightly power hungry
The RE0 has been available for several years now and therefore it has had time to penetrate the Head-fi community and generate a range of comments on it's performance as a moderately-priced IEM. After reading various threads and reviews myself, I came to the conclusion that their qualities probably outweighed their liabilities and recently purchased a pair. After a month with them, was it a good decision? In a word, yes, but with a few caveats.
Off the top, I would say that the RE0 is probably not going to match everyone’s listening preferences. The often repeated comment that they are bass-light, is generally a fair statement. Nonetheless, when listening to music with isolated bass, the RE0 quickly demonstrated that it was capable of delivering accurate bass easily. What others have said (and with which I completely agree) is that the RE0 lacks bass impact or sustain. In a musical context, therefore, the mid- and treble frequencies of the RE0 can dominate the bass producing what is often referred to as an analytical sound signature. Is this enough to kill the RE0 as good IEM? Not to my ears, because I don't listen to music that is overly bass-centric. Small group jazz, acoustic roots and blues, female vocal, solo piano, classical guitar are just some of the genres that will shine through the RE0. What the RE0 does deliver in spades is pin-point clarity of instruments and vocals that are accurately imaged and presented on a surprisingly wide sound stage.
Several other points are worth mentioning regarding the overall sound quality of the RE0. Indicative of any quality headphone or IEM the RE0's benefited substantially by:
a burn-in period
a quality source
enough amp support
These factors unquestionably affect all IEMs, but I found this to be particularly true for the RE0. Right out of the box they did not impress, especially from a portable DAP playing low bitrate files. However, within 20 hrs. of burn-in the sound quality became much more balanced, the bass less attenuated in its presentation. Music files also need to be at a high bitrate (320k - 350kbps), if you’re not going to a lossless format. Although the RE0 is marketed as an IEM for portable devices, its nominal 64 ohm impedance indicates that it really benefits from additional power beyond what my Sansa clip can provide. This is based on how much better the RE0's sound through my Sony laptop and makes me consider that the RE0 would scale-up nicely with a desktop amp.
Regarding other issues like build quality, in ear comfort and noise isolation, I have had no problems. Every IEM requires a bit of experimenting to get the best fit. The bi-flange tips are quite soft, although for me the medium rubber tips and worn over-the-ear provided the most comfort. Noise isolation, however, is only average at best, which may be an issue if you intend on using them in a noisy environment.
At their currently listed retail price of $79.00 from Head-Direct, I believe that in the right musical context, the RE0 continues to provide outstanding value in a IEM.