Lets start off with the pros. When first out of the box they sounded great, good bass and slightly crushy highs but after a mere 10 hour burn in they sounded great, hard (but not thumping) bass and excellent no distortion highs. I mainly listened to EDM, house and hip hop and those genres sounded great in the ckx9is but vocal tracks from Ed Sheeran and Sam Smith wasn't at all shabby. Also, the ckx9is and great detail and soundstage versus the s4i rugged which i had previously and for the same retail price the ckx9is is by far a better sport iem.
 
Onto the design and comfort, the only issue i found was finding the right fit as personally i do not like foam tips but was a nice addition and the c tip addition helps with isolation and fit as the earphones are large and heavy but does have adverse affects on small heads as because of its size, it pushed the tragus of my ear forward slightly. Also the in line mic is separate to the volume control of the device which confused me when i had the volume very high on my phone and was quiet in the iem. Also any slight movement of the slider or button would cause disruption with the channels (making one ear sound quieter than the other) which was annoying but a fairly unique feature. The l shaped plug was a bit large to fit perfectly with my iphone case but it did not affect the sound and the cable itself is very good but not fully untangleable.
 
Overall a great headphone for its price range and would recommend to any sort of edm/hip hop listener

Firstly, this is my first review on this site so this may not be to the accurate Head-Fi standards. Out of the box, it took me a while to find the perfect fitting an i opted for the large and long ear tips. My first impression were poor, there was virtually no bass and my old pair of EarPods could have sounded better, but i noticed it had low distortion compared to the EarPods. After about 4 hours of burn-in the bass was present, and quite detailed but just lacking the volume. If the artist wanted bass in the song, the S4i Rugged would perform, but in other songs, the bass was not as dominant as other in-ears i have tried. The mids and highs were quite pleasant, vocals sounded nice and at a price of £40 (half-price on amazon) it was a good bargain. But at the full £90 price tag, it is not worth it. Another thing, i usually like to have my in-ear cables underneath my hoodie when i run and the mic design made it impossible to pick up the phone or even change volume and the cable sound was unbearable if i didn't have it underneath my hoodie. But all in all, these are quite pleasing but if you like bass, steer away from these earphones