The iems arrived safe and earlier than expected. Upon opening and testing the unit, I noticed that one of the unit's rotating housing (nozzle) is slightly loose compared to the other unit. After doing some diggin on the net forums, I saw that some people have a slightly loose housing while others don't.
The loose housing doesnt rattle when playing loud but I wonder if the sound if affected by the loose housing.
Also I did the modification suggested by James444 at superbestaudiofriends and they sound great for the price.
ButtClenchBANDITI purchased the FDX1s, and one of the IEMs has a wider gap where the housing rotates, and it wiggles a little more, but after months of critical listening, including swapping sides, I have not been able to detect any effects on sound. It seems like the few people who received defective units had easily noticeable improper sound.