The iFi Nano iDSD may not be a looker and it may have a small package but it delivers performance you'd expect from regular desktop DACs at an unbelievable entry level price.  In addition to that, if you have to think twice about getting a -700 portable amp/DAC that supports iDevices - go for the Nano iDSD and know that it rivals those devices at a price that is 3 times lesser.   
 
This is a transparent DAC that delivers a refined and natural sound that is difficult to find at this price point.  Instruments are rendered realistically and vocals are full of texture and nuance. There's just a wholesome-ness and balance to the sound that reminds me of high end British hi-fi.  The built-in headphone out can easily drive IEMs with a black background at all volume levels thanks to its potentiometer-less implementation of volume control.  It can surprisingly drive LCD2s well enough on its own but what really shines here is the DAC and feeding an amp will be the way to go.  
 
The Nano iDSD was an impulse buy from me - I was at a headphone shop looking for IEMs, spent some time auditioning with the iDSD and ended up taking home both a brand new pair of IEMs and the iDSD.  I was that impressed by them and have not regretted my purchase at all since.

When my 2 year old DBA02 mkii's lost left channel signal strength, I needed a replacement, pronto.  I took note of some good sounding < IEMs from |joker|'s list and headed off to the nearest headphone store - to tide me over till I went custom, so the idea went. (I totally agree with |joker|'s 9.2 assessment of SQ on the DBA 02 mkii, fyi)
 
As it turned out, they had none of the phones on my list but they did have something new - the TBA 04 - that had only just come in for a few months.  I'd brought along my DBA 02s to A/B the TBA 04s with, which I auditioned on an iFi iDSD nano AMP/iDevice DAC, with ALACs from my iPhone.  
 
On first listen, the TBA 04s were quite similar in sound signature to the already excellent DBA 02s - accurate articulation, palpable soundstage (for IEMs) and balanced sound.  But where the DBA 02s could get a little thin, the TBA 04s were full and flawless.  Where I sometimes wished for a little bit more bass in the DBA 02s, the TBA 04s never left any doubts.  This is something that I'd attribute to the TBA 04's 3 balanced armature drivers compared to the 2 in DBA02 mkii.  
 
2 weeks later, with some solid use, my first impressions stand - with more observations:
- On high intensity orchestral tracks, the TBA 04s are remarkably close to full-sized cans for fullness and power and handle them with aplomb
     - Carmina Burana: O Fortuna and Carmen Suite No.1: Les Toreadors are good examples
- These phones are good with resolving minute details and yet keeping the treble in line
- There are no weak genres on the TBA 04 - though that may just be my preference for transparent/uncolored sound
- Instrument separation in the soundstage is superior in the TBA 04, compared to the DBA 02 mkii
- They still sound pretty decent unamped, running straight out of an iPhone 5 - just without the extra control, presence and resolution that you get with a separate dac/amp.  It also means that they're very easy to drive
- I miss the solid cable from the DBA 02
 
Should you buy it?  Well if you're into transparent sounding hifi, it is a resounding yes.  
 
 
Edit:
3/27/2014
I'm writing this now because having had my LCD 2 cables chewed out by my cat (he's more dog than cat), I've had plenty more listening time with the TBA 04.  
 
In particular, I'd like to point out how well instruments are separated out in The Roy Hargrove Quintet's - Strasbourg/St.Denis track.  The detail extraction is revealing - the bass celloists hands/fingers as they slide across the strings, the twang of the bass cello strings against the body.  And when compared to my full headphone LCD 2s - there's a wholesome quality in these IEMs akin to what you get from full sized cans.