Pros: Sensible and comfortable design, balanced sound quality, fantastic value
Cons: Overly large plug, sparse included accessory selection
Along with the summary below, I have posted a Youtube video review of the RE-400. If you like the video, check out my channel for more reviews :)
The RE-400 has a sensible, well thought out design. Of special note is the half-rubber / fabric cord which cuts down on microphonics. The RE-400 is comfortable to wear with cable up and the metal earpieces seem quite durable. However I find the plug to be overly large and can be difficult to accomodate in some pockets. The included accessory selection is quite poor, with only a few tip sizes included. Unfortunately I could not get a good seal with any of the tips and ended up using Sony hybrids, so please bear this in mind when reading the following sound impressions.
The RE-400 has a neutral, smooth sound with perhaps a slight emphasis on the lower mid-bass, though this is certainly no bass head earphone. Everything is very tight, very fast and this is truly an amazing performer - not even considering the price at this point. Soundstage is not immediately very wide however, and people after something with a wider soundstage should perhaps look at the Sony MDR 7550.
I think despite the small issues I have with the RE-400, it offers absolutely stunning value at the $99 price point and really lays down a challenge to other manufacturers. As a neutral IEM the RE-400 stands shoulder to shoulder with other good dynamic options like the VSonic GR07 and Sony 7550, and does it at a lower price and better ergonomics. I absolutely applaud HiFiMan for the sharp pricing on the RE-400 and would heartily recommend it to almost anyone.