Disclaimer: this sample was purchased at my own expense
After a sudden discontinuation of their introductory model RE-0, HiFiMAN comes up with a new pair of IEMs, RE-400. This model features new innovations, such as an OFC-copper cable, a magnesium housing, and most notably, a titanium-absort diaphragm. Coming with a price tag of $99, RE-400 is slightly expensive than its predecessor, which was $79.
As previously stated, HiFiMAN RE-0 is one of the IEMs with stunning electroacoustic characteristics. If RE-400 turns out to be overwhelming RE-0's performance, it will surely be considered as a very successful transition done by the manufacturer.
CON: A slight mid-range mismatch possibly due to the difference in stratum of titanium.