These IEMs are extremely tip dependent. Ocharaku voiced them (for some reason) with Comply-style tips---ie. "foamies"---in mind, and while I'm generally not a fan of these kinds of tips, using them really makes this IEM a lot more enjoyable than using silicon ones. They don't blunt its sound as with most IEMs, but rather tame the treble enough to where it's on the outskirts of the acceptable zone for me. Still the treble is going to be peaky irregardless, and these are really fatiguing. The SUI version is worse than the KAEDE in this respect, as the treble is rougher and less refined overall to my ears.
At the other end of the spectrum I cannot fathom anyone finding these bass light with the right fit. They're actually some of the punchiest IEMs I've heard with some really hard hitting mid bass that is surprisingly well controlled given how copious it is. Overall a pretty obvious U-shape signature. What draws me to the Flat4s personally is their sense of detail and layering, which to my mind ranks toward the top of universal IEMs I've heard over the years.