I am new to head-fi and this is my first ever review. Basically I joined head-fi to read people's expert opinions on different products, as I'm not an audiophile and do not know much about the science of all the media devices and headphones being reviewed. Here I would give some simple observations I've had with Fiio X1. Previously I used to listen to music using my HTC One M7 and I thought that DAP's won't make much of a difference to the sound quality which matters for me the most (sq > ui, for me), until I got one on my cousins suggestion. And for my surprise, it made a lot of difference, something which is not easy to explain for me as I don't understand much of the audiophilic terms used during reviewing a product.
 
In-ears used:
- Shure se215
- Monster Copper Turbine Pro
- Dunu dn1000
- Logitech ue900
 
Music played:
- Time by Pink Floyd (24/96 flac)
- Hotel California by The Eagles (24/96 flac)
- You shook me all night long by ACDC (16/44.1 flac)
- Turn the page by Metallica (16/44.1 flac)
- Fear of the dark by Iron maiden (16/44.1 flac)
- Trains by Porcupine tree (16/44.1 flac)
 
I've mentioned these in-ears and music files with their formats as I compared the X1 with my friends X5 and could barely differentiate the sound quality and sound stage (A mere difference of 19-21 as one can say in short). I prefer it over X5 because of its weight and size (portability), whereas X5 is too bulky for my pants.
 
Rest I've written my critical findings in the pros and cons section. Hope this basic review could be helpful for the ones who are still in a fix to go for the X1.