I'm like one of the biggest Flat4 fanatics on head-fi. I have the SUI and KAEDE, and while the latter is a gorgeous piece of kit that is definitely an upgrade in the materials department, I'm not so sure it's a big upgrade in terms of sound. In fact, it sounds quite similar to the SUI to my ears, main difference being slightly less glare up top and slightly more bass heft below. While I appreciate the better upper-end, I don't think the SUI needed anymore bass! The KAEDE can be a little overwhelming on certain tracks. But really, both are exquisite and beat the pants off of most other IEMs for me personally, especially in terms of refinement (no nasty resonance), detail extraction, and dynamics.
As for the Donguri, I hate to say it, but they kind of remind me of those awful Thinksound RAIN earphones on the outside, though I'm sure the craftsmanship is superior. Knowing Ocharaku, the engineering on the inside will result in a good sound too.
MuppetFace, I can't have enough praise for the SUI. Gosh. They're marvelous and yet so under-the-radar! I felt like the sound is so natural, like I'm really hearing the instruments "as how they sound". While vocals have taken me aback due to the un-intimate distance, I found that almost everything is so clear and Real. The only other experience which almost relates to the feel of "realness" is the FAD FIBASS, with a much more heftier price tag, a greater amount of bass, and almost the same aspects in sound quality. I heard the FitEar as well, still think they lack the transparency (Not that they are any bad, maybe my brain needs more burn-in towards that kind of sound).
Yeah, the RAIN series. Well, I wonder how it "tornadoes" into the ear, and how it affects sound quality.