The KB EAR Diamond, which uses a diamond-like carbon coated PET diaphragm dynamic driver, is hands-down the the best IEM I’ve heard under $100 (it currently retails for $79). It has excellent technicalities and a clear and engaging tuning. Other IEMs I have heard in this price range, like the Shozy Form 1.1 and Dunu DM-480, are simply outclassed.
Its sound signature can be described as a slightly exaggerated Harman Target. Compared to the Tanchjim Oxygen, another IEM with a DLC dynamic driver and a Harman-ish tuning, the KB EAR Diamond has more bass and more elevated upper mids between 3-6k. If you think that a Harman-tuned midrange is thin or shouty, you should pass on the Diamond. Otherwise, I highly recommend it.
I will update my review with a comparison to the Moondrop Starfield at a later date.
You can read my full review, with additional images, measurements, and optional EQ tweaks, on my blog: