Completely agree on it being a waste to run the i4s direct from a phone, was merely making the point that it is possible and that it will sound fine, just not nearly up to their potential.
I got my REI direct from Cozoy and I think it is a great little piece of kit. I have been working on a full review, but have posted impressions over in the rei thread. Generally, with low impedance iems or headphones (including isines, i4s, and Mr. Speakers Aeons), I find it comes within a whisper of the level of performance soundwise as my mojo, but it is something with the footprint essentially the same as 2 housekeys stacked on top of one another. The mojo provides a little bit better instrument separation, airiness, and soundstage (and obviously has more power), but the REI is pretty much on par in terms of bass and treble extension, and quality, midrange sweetness, and musicality. Like the mojo, the REI is almost never shrill in the treble while still maintaining detail, and in the REI may even be a bit more "fun" than the mojo in some tracks. Given how tiny the REI is, the fact that it doesnt have a battery, minimally affects battery life on my iPhone 7 plus and that it works out of the iPhone without a cck, it is pretty great. I've stuck a flat fridge magnet on the back of my rei which makes it stick to the back of my iphone (I have a metal plate on my phone for a magnetic car mount), and end up with a rig that in my pocket is indistinguishable in size from my iPhone itself and sound quality that out performs my dragonfly red or Oppo ha-2. With the i4s, I have to turn the volume up to about 70-80% to get it to what I would consider loud, but it definitely can drive them louder than I would want to listen to them. Again, the mojo provides a bit better instrument separation and a larger soundstage, so for the i4s, which I don't use as much while I'm walking around I am reaching for it more than my REI. But for what the REI is, what you get is shockingly good.
