I have received i5 as a part of its EU tour.
 

 
 
UI
 
I like the design and UI a lot. It is Android 4.4 based so not the latest but will do. It also has ability to download 3rd party apps (as opposed to some other Android players like Opus #2).
I use 3rd party apps to sync my desktop PC (iTunes) with the players I own. It copies not only song but bi-directionally syncs metadata like ratings, play count, skip count, last play time etc.
It helps to create a dynamic playlists like "often played but not rated yet" or "highly rated but played long time ago".
I was happy to see it working with the Cayin.
 
The interesting part of UI is that the special music-centric launcher is used. There is no desktop. You can swipe to the left to open a menu where you can find some settings and 3rd party apps.
Google Play works just fine when you enable the WiFi. I have not noticed any interference from WiFi so it is well shielded.
 
The UI is very well designed but sometimes hangs. I had to restart the player from time to time. I am sure this can be improved by future firmware upgrades.
 
Design
It feels solid and handy. Has physical buttons which is a plus.
The leather case I received with the Cayin protects most of it but makes the use of side buttons a bit more difficult.
 

 
 
Sound
I would rate it above Samsung S6 phone but below Sony ZX2, Onkyo DP-X1 and iBasso DX100. Those 3 are more expensive though.
Cayin is smooth and warmish so may pair well with headphones you find a bit too harsh or too bright.
Its soundstage is intimate, narrow and sometimes a bit at the back of you head. I must admit I prefer more "in front" presentation when the sound is positioned more in front of me.
The soundstage has nice layering in terms of depth. If you carefully listen you can distinguish the layers of presentation well.
I liked the Cayin's tonality: the instruments sound natural and you can distinguish their tone well. I would even say that in the tonality aspects it beats the ZX2.
ZX2 wins in terms of clarity. Cayin sounds a bit muddy when put next to it.
What kills the music aspect to me is the decompression artifacts. From time to time you can hear loud squeaks like the audio file was broken.
I use alacs (Apple lossless format) that work well on S6, ZX2, DP-X1 and DX100.
 
Cayin i5 vs Sony ZX2 with Denon AH-D5000

1. i5: natural sound, soft
2. ZX2 clearer and deeper bass

1. Diana Krall / Peel Me a Grape: more echo / room feel on i5, more bass and clarity on ZX2 - ZX2 wins
2. Hurvitz / Overture :i5 more naturally sounding, ZX2 drier - i5 wins
3. Bonnie Tyler / Total Eclipse: i5 sweeter vocals, more natural instruments, ZX2 - crispier - i5 wins
4. Pink Floyd / High Hopes: i5 more natural, warmer and smoother, ZX2 - less natural, colder, harsher but also crispier /cleaner.
   If you prefer relax and smoothness over detail and clarity i5 is your pick.

 
Cayin i5 vs Sony ZX2 with 64 Ears A12 CIEM

1. The Handsome Family - Far from any road: i5 a bit dull and foggy, good resolution, narrow soundstage, ZX2: much cleaner, wider soundstage, more 3D, more details, ZX2 wins
2. The Cranberries - Zombie, i5: more natural, less clean, more intimate
3. Florence + The Machine - What the water gave me: ZX2 nicer bass texture and instruments separation in intro, cleaner, a bit of sibilance, i5 no sibilance, a bit deeper but narrower soundstage

 
Cayin i5 vs ZX2 with Audeze Sine

1. Zaz - Les Passants - ZX2 crisp, good instruments separation, i5: less 3D, more in the face, a bit foggy, ZX2 wins
2. Big Bad Voodoo Daddy - Please Baby - i5: narrower but deeper, more natural but less crisp - ZX2 wins

 
Cayin i5 vs Samsung S6 with Denon AH-D5000

1. Adele - Someone like you - S6 a bit harsh with modded D5000s. i5: deeper low tones, piano is clearer and more present, voice even more in front, more 3D, i5 is a clear winner
2. Birdy - Skinny love - S6 is more dull and foggy, plays from distance, a bit sibilant, i5 is clearer and more present, has more 3D soundstage, and better positioning of instruments, less sibilant - i5 is a clear winner

Cayin i5 vs Samsung S6 with 64 Ears A12 CIEM

1. Christina Aguilera - Express - S6 has flatter presentation, but is a bit clearer and has blacker background, i5 is foggy with Low Gain, switching to High Gain improves a lot, but still the background is greyish, soundstage is better, instruments are more natural - no clear winner - depends what your sound preferences and priorities are
2. Morcheeba - Lighten up - again S6 is a bit harsher, flatter and clearer, i5 is more relaxed, smoother, natural sounding, more 3D but a bit foggy

Cayin i5 vs Samsung S6 with Audeze Sine

1. Leonard Cohen - Waiting for the Miracle - i5 is natural sounding, not sibilant, warmish, more 3D but with greyish background, s6 has a bit too much of low tones which dominate the mids - i5 is clear winner
2. Jacques Loussier - Toccata and Fugue in D Minor - i5 has nice punch, natural sound, relaxing sound, misses on ultimate clarity, s6 seems faster, shows nicer texture of low tones, has crispier high tones - it comes the cost of limited soundstage and less natural sound

 
General comments

1. more power than Sony ZX2 - especially with Audeze Sine outdoors
2. occasionally hangs - restart needed (hold power off for a few secs) firmware 2.0
3. music settings -> digital filter options: short delay slow roll off - makes sound sharper and cleaner IMO + adds some “echo” effect / room feel
4. good battery life, but charges slowly
5. takes up to 2 seconds to start playing
6. alac playing problems
7. tested with 3rd party Apps: Rocket Player and iSyncr to auto-sync PC/iTunes and the player

 
Summary:
If you're looking for a nice DAP which is a clear upgrade from a phone and has warm sound you should definitelly give i5 a listen.
If you prefer natural tone of instruments over the clarity you should shoot for the Cayin i5.

I received a test Caying N5 as a part of the tour, used it for a week.
I will not be posting a pictures because there are plenty of them already but will try to compare Cayin to my phone and other DAPs, describe what I heard and try to rate it.
Of course all my opinions and rating here are subjective and you may choose to dissagree.
 
I used low gain setting on the N5 as the presentation was "less in the face" which is something I generally prefer.
 
Other equipment / settings used:
- 1964 Ears Adel A12 CIEMs (TOTL)
- Denon AH-D5000 closed headphones (easy to drive, bassy, quite wide scene for closed cans)
- Samsung Galaxy S3 (i9300, Wolfson DAC) with Boeffla sound enabled in kernel
- HiFiMan HM-901: low gain
- iBasso: DX100: mid gain
 
A12 / Allan Taylor - Colour to the moon
vs i9300 much wider and a bit deeper scene, more organic and lively, more smooth, bit brighter
vs DX100 less crisp highs, less organic, narrower scene, not so lively, equaly smooth
vs HM-901 less crisp highs, less organic, a bit narrower scene, not so lively, equaly smooth
ratings:
- i9300: 1/10
- N5: 5/10
- DX100 9/10
- HM-901 8/10
 
A12 / Big Bad Voodoo Daddy - Please Baby
vs i9300, N5 had: scene more consistent left-to-right, wider, tonality: a bit brighter, exposed / a bit tiring higher mids / lower highs
vs DX100, N5 had: shallower scene, less differentiation of instruments tone, was much brighter, was a bit artificial
vs HM-901,N5 had: a bit shallower scene, less diffrentiation of instruments tone, was much brighter, didn't hit so tightly
ratings:
- i9300 1/10
- N5: 3/10
- DX100: 9/10
- HM-901 7/10
 
D5000 / Allan Taylor - Colour to the moon
vs i9300: scene more centralized but wide, more 3D, a bit too bassy, mids seem loosing in favour of highs and lows (V shape?), highlights left channel which is brighter than right on this recording
vs DX100, N5 was: less 3D, a bit too bassy, less balanced left-to right (DX100 doesn’t highlight brighter left channel any more), feels less relaxed
vs HM-901, N5 was: less 3D, less 3D, a bit too bassy, a bit less balanced left-to right (901 does highlight the brighter left channel less then N5 and more than DX100)
ratings:
- i9300: 1/10
- N5: 3/10
- DX100: 8/10
- HM-901 9/10
 
D5000 / Big Bad Voodoo Daddy - Please Baby
vs i9300, N5 was: more lively, hits harder, feels much more in control, has wider scene, better tone of instruments, has higher scene (up/down)
vs Dx100, N5 was: a bit less bassy (positive) , less relaxed, has narrower scene, has taller (up/down) scene, more “in the face” which is something I usually don’t like, but I liked it with N5 on this piece of music, brighter, a bit less veil clearer
ratings:
- i9300: 1/10
- N5: 6/10
- DX100: 7/10
- HM-901: 8/10
 
Software/UI stability ratings:
- i9300 10/10
- N5 10/10
- DX100: 6/10,
- HM-901: 4/10
 
UI features/usability ratings:
- i9300: 10/10 (Tidal, Spotify, music ratings, great display, long batter life)
- N5: 5/10 (I missed music rating / playcount features I love on i9300 and DX100)
- DX100 8/10,
- HM-901: 5/10
 
Other remarks:
- places accent on highs
- highs are revealing on harsh tracks, edge of harshness
- the rest smooth and buttery
- mids may be a bit recessed / foggy
- nice subbass
- shines on well mastered tracks
- soundstage is wide and tall but not very deep,
- plays a bit "in the face" but still pleasant,
- is musical,
- serious improvement over i9300,
- more direct and crisper than DX100,
- pause/play switch takes up to 4 seconds
- one of SD slots didn't work at one occasion, the same card worked fine in the other slot; no problem with first slot on the second day
- wasn't albe to test it as PC USB DAC due to driver installtion problem
- control wheel needs some patience (a bit like on HM-901)
 
In generall I find the N5 to be an enjoyable DAP which is not at the TOTL level however is definitelly a step up from a good sounding phone and has a very good price/value ratio.