The KZ D-Fi has really good tonality (neutral with sub-bass boost) and is closer to a Moondrop or Tanchjim curve than the usual V-shaped KZs. Timbre is also very natural.
Graph of the D-Fi via an IEC711-compliant coupler. 8kHz is a coupler artifact peak:
The tuning switches are mostly a gimmick, with just a 4dB difference in bass between the most extreme of switches. In essence, it might be wiser to get the non-tunable version of the D-Fi (which is cheaper), and the non-tunable tuning corresponds to the most bass-lite graph.
The D-Fi however, is extremely weak in technical chops. Soundstage is compressed in all three dimensions, and imaging, instrument separation and micro-details are abysmal. I think some $20 USD IEMs beat them in technicalities easily, and this holds the D-Fi back from greatness.