If you're looking for an IEM that is highly engaging and smooth with a strong bassline, full mids with superb vocals and very refined and elegant treble then the C9 Pro is definitely among the top options especially at its price point!
If you’re looking for a smooth and fun sounding IEM with strong bass, beautiful mids and lively treble that does not compromise on fundamentals and is showing top performance in their price bracket, the U2 is definitely worth an audition! There are few gems in the sub 500$ range and the U2 is one of them in my book.
If you’re looking for a neutral IEM with top notch detail retrieval, great soundstage and accurate tone that provides a fatigue free experience without breaking the bank then the U9 is definitely an IEM you should try! If you’re looking for more bass kick, sweeter mids and sparkle, then other IEMs of the StealhSonics will be of interest.