I picked up an FD01 a while ago, compared the FDX1 and FD01 extensively on bassy tracks for a few hours this week. I can confirm what many here noticed, that the bass is definitely tighter and more defined on the FDX1. Now, it's not like a gigantic difference, but the difference is there and noticeable. It's a little less present and impactful in the bass compared to the Moondrop Kato, but otherwise the quality is very similar. The FD01 on the other hand, does not have the same quality bass as the FDX1 or Kato. I am using a slight EQ boost on both the FD01 and FDX1, the FDX1 extends better in the sub bass with more rumble, and with sharper mid bass attack/punch, regardless of how much I EQ the bass. Using the same tips and filters on both for this test (white steel stock nozzle, Moondrop Spring tips). Mids and treble sound pretty much the same. I also have to point out that on my particular FD01 earpieces, the quality control seems to not be as good as the FDX1. When rotating the nozzle, it feels scratchy on the FD01. I also noticed a slight channel imbalance in the bass below 150 Hz. I didn't have any of these issues with the FDX1. I do have to wonder if Drop + JVC will ever bring these back, they have been out of stock for quite some time now.