Pros: Beautifully built hardware, hardware music controls, generally good interface
Cons: Reflective LCD, relatively slow CPU, noticeable hiss with some equipment, does not meet 24/16 bit audio spec?
I will try to keep this short.
Firstly, to disclose: I purchased the NWZ-ZX1 with a 25% off discount coupon given to me by Sony Australia after attending a demonstration event for their high resolution audio products. I was invited to this event in my capacity as a Youtube reviewer.
The Sony NWZ-ZX1 is a beautifully built piece of hardware. Hardware music controls are wonderful. The interface is by and large easy to use.
The LCD is quite reflective and not particularly bright in direct sunlight. This seems to be because it appears Sony did not use a bonded glass display assembly like modern smartphones, which causes reflections due to the air gap between the LCD and the glass.
The interface and drag and drop music transfer is quite easy to use. However the default music player exhibits some lag when scrolling through albums rapidly.
Here is my video about the physical aspects of the player:
In terms of audio performance, it is suggested by Soomal's RMAA results http://www.soomal.com/doc/10100004953.htm that the ZX1 has a noise floor that is so high that it cannot deliver the dynamic range necessary to take advantage of 24 bit audio, and may not even have an effective bit rate to deliver the theoretical maximum 96 dB dynamic range of CD quality 16bit audio. Whether or not 24 bit audio actually matters, it is disturbing to see that Sony is marketing the player as a flagship high resolution audio device when it cannot seem to deliver what it says on the box. I would love to see more results published for the ZX1, but for reference comparison the ZX1 does not seem to do as well as an iPhone 5S http://www.soomal.com/doc/10100004450.htm or HTC One M8 http://soomal.net/doc/10100004976.htm, which are both smartphones that do more than the ZX1, have better underlying hardware, and cost similar amounts.
For my own subjective comparisons, I took a ZX1 and my iPhone 5S and volume matched them within 1dB using a Sescom iPod A/B switch and a Zoom H2n recorder. I then listened on a variety of equipment. On my Sony XBA-H3 and Sennheiser Amperior, a subtle hiss was noticed on the ZX1 that was not apparent on the 5S. On the multi balanced armature Nuforce Primo 8 review unit I have on hand, the hiss is very loud and noticeable. Again, this hiss was not audibly present on the 5S.
Here is my video depicting how the volume matching was performed and some of my notes about the audio performance of the ZX1.
Apart from the hiss, the two players sound very similar. Both sound very neutral and detailed.
Based on my findings I cannot recommend the Sony NWZ-ZX1. It is very expensive for a device that performs worse than similarly priced smartphones, and yet does less and is more difficult to carry around because of its unusual physical shape.
I think people who know what I have written in the past know that I am a big follower (and maybe a hyper critical one) of Sony's audio gear. I am disappointed to see Sony embrace a marketing push for high resolution audio while delivering flagship products that fail to live up to that spec.