I recently picked up an ASUS Zenfone 5 and 6 from fasttech. The price was right ($150 for the 5 and $260 for the 6). Fasttech noted that the phones could be configured in English, but once they arrived, it was obvious that that was not the case. From Fasttech, the phones have China Telecom firmware installed, and it was not possible to simply change this. Luckily, ASUS provides firmwares for these phones, and they come in three flavours: CUCC, TW, and WW. WW is the english version, and WW apparently stands for 'world wide'. Unfortunately, the phone region locks to the firmware type that it is shipped with. That means that the phones from fasttech are basically useless unless you can read Mandarin. I put the following guide to help any new Zenfone users:
If there are any issues, please let me know.