Update on the KD Duo/Yinding Clone. Good news! KD responded to my inquiry about buying the driver used in sku#S023788 (the "10-step user programmable" one reviewed by ledoman). They will sell the driver for that light for $8. They also reminded me that for my 4.2v version light the LEDs would need rewired to series (I appreciated hearing this from them as it showed me they had some knowledge on what they were telling me about driver replacement). If interested, you would just have to contact them and say you wish to purchase the driver used in bike light sku#S023788.
-Garry