Pros: Very musical sound, highly detailed, fit, jaw-droppingly fancy case, good bang for buck
Cons: Fit, looks, poor stock tips, microphonic cable, kind of fragile, lacking a bit in upper mids
As soon as I read Shigzeo's review of these, I knew these might just be the phones for me. I was a bit worried about the fit since I have alien ears, and no IEM has ever been completely comfortable for me. Although it's not too comfortable wearing them like you're supposed to for me, I've found that wearing them upside down with cable over ear makes them the most comfortable IEM I've ever come across. The downside is that I trade airiness for thickness in the sound and it looks funny, but no other earphone has been this comfortable. For sure though, the bizarre fit will vary from person to person and so I list fit as both a pro and con.
For sound... the title says it all. I would describe the sound signature to be warm - mid and bass centric with smoothed out highs. About the bass... ah yes, the bass. It's wonderful. I think the bass pretty much holds this phone together. It extends very low and has thunderous impact, but still slots in perfectly with the rest of the sound and rarely bleeds into the mids. This is a definitely a headphone for lovers of plentiful, quality bass. Additionally, soundstage is quite wide so epic orchestral music sounds fantastic. Mids are just as great although certain higher pitched female singers or female opera singers can sound a bit lacking in quantity (described as a "suckout" by shigzeo) compared to some of my more neutral phones. I'm a big fan of female vocals but I've still been happily using these nearly every day for about a year so this isn't too much of a drawback. Highs aren't piercing and well balanced with the mids and lows, as long as they're paired with a neutral sounding source. Timbre is great (though I'm guessing the FX700 would dominate it here...) and drivers are not as fast as my HJE900 but should be fast enough for most music. I listen to a wide range of genres and the Radius renders every genre beautifully, with special mention to acoustic music (guitar and piano sound so real), all kinds of electronic music, hip-hop, pop, and slower-paced rock. Compared to the HJE900 (which still represents incredible value), the Radius seems to give the sound that final touch of realism - a definite step up.
Value and audio quality ratings are subject to change, as these are my highest end IEMs at the moment. There are many drawbacks to this phone but I believe the sound alone already over-qualifies for the price I paid. For a full size headphone comparison, I haven't heard the HD650, but based on my HD600 and what people say about the 650, I would say this resembles the HD650 for sound signature. And about the HD600, I was actually a bit disappointed when I got them. Even though the HD600 sells new for double the price of the Radius, I found the sound quality of each to be more or less on par (with my gear), with highs and imaging of the HD600 to be slightly ahead, mids to be about the same, and bass on the Radius to actually be present (quality about the same, though). Both of these headphones have their uses for me, but the Radius will still be my go-to headphone for enjoying and rocking out to music.
edit: So the rumours (fact) about the HD600's scalabiltiy were true... I upgraded my amp to a SOHA+jisbos and holy ... there's no longer any contest between the HD600 and the Radius.
However, it took $300 amp on top of my dedicated DAC to declare a sure winner... not very fair. In the portable territory, the Radius DDM has this for sure.
edit 2: I can now pinpoint this earphone's greatest strength: its ability to make EVERYTHING sound good. I've never come across a headphone that sounds good with so many genres and both good and bad recordings. This is great... I hate revealing headphones. I can listen to good music without being tied down with poor recording quality.
2012: Still my favourite earphone, even over technically better earphones like the FXT90, EX-600