Pros: Subjective sound quality; form factor, build & looks; instant on/ off & straightforward controls
Cons: Pricy. Limited features & no screen - no cons for me, but reported as such by a number of others.
I have the player for almost a year.
I do not have experience with other upmarket DAPs, but I am familiar with Apple products, Sansas and some stationary gear (a bunch of open headphones and speaker setups).
Tera Player together with Ultrasone Edition 8 or beyerdynamic Tesla T5P remains my favorite setup.
Actually I prefer it to my stereo (which is decent), - it's observation based, as I hardly switch on the stereo lately
(available contents being identical, - CD/DAC is connected to my Mac, so there is everything what's on Tera & more).
Subjective sound quality is very natural and involving, and Tera Player virtually does not create any listener fatigue (depends on the recording though).
Ed. 8 work fine for me with almost all musical material, I only really prefer T5P for jazz and classical (it is great to listen to most stuff via T5P - just different if compared to using Ed. 8).
Other cans (listed below) sound good, too (obviously no meaningful comments can be made in the cases when Tera Player's output power is too low), but both Ed. 8 and T5P clearly have an edge.
The subjective differences between HD 25-1-ii, DT 1350, Ed. 8 and T5P seem to be more noticeable when those cans are used with Tera Player than, f.ex., Sansa Fuze (which is a great little player in its own right), - but this is totally subjective.
I have no clue about measured performance.
Tera v.0 is loud enough for me with Ed. 8 (although in this combination I use Tera Player at max volume now and again), T5P, HD 25-1-ii, DT 1350, MDR V6, CAL!, and enough and to spare with PortaPro.
It is hardly usable with HD600, and way too quiet with K701 and DT 880 (600).
I do not use IEMs, so I cannot comment.
Battery capacity seems sufficient (never ran out of power so far).
Form factor is perfect for me, as is player's instant on/off and simple interface.
N.B.: it ain't got no screen, and it plays only WAV files !!!
It's got five buttons and two 3.5mm jacks (and there is a difference between the output of those).
It plays, it stops, it goes to next / previous song / album / artist, it's got a volume control and it does random. Latter is as random as the file organisation on a card allows it to be (I can live with it).
Dropped once so far, - apparently no damage.
Price for me is justified by the level of subjective satisfaction which this player delivers.
I highly recommend Tera Player to anybody who looks for a very good sounding portable solution, - particularly for those located in Europe, where warranty provisions and pricing of Chinese top-tear DAPs so far have not been as attractive as they are across the pond.
I can well imagine others being put off by the absence of GUI and certain features; moreover, so far there has been rather scarce information about the measured performance of the player, -
give it a listen though!
EDIT fall 2013:
I still imensely enjoy the player, nevertheless I am dropping one star given that Charles recently doubled the price.