I purchased the kit as it was on sale, but just needed the Obsidian 25 watt solar panel. I did not need the included PWM controller, as I already had a MPPT controller.
Before purchasing I did an online Chat with Zamp to verify compatible with my existing Victron BlueSolar MPPT 75/15 charge controller.
Problem - The Victron MPPT controller requires the solar panel output voltage to be 5 vdc greater than the battery voltage in order to initiate charging. My battery is a Battle Born 100 Ah LiFePO4. The Battle Born battery bulk charges at 14.4-14.6 vdc. The Obsidian 25 watt panel has a maximum voltage output of 18.4 vdc (mine measured 17.38 vdc). Because of this charging only occur when the Lithium battery is substantially drained, and the battery will never reach a full charge.
By replacing my MPPT controller with a PWM controller the system now functions correctly. The PWM controller is less efficient but only needs a +2 vdc voltage difference. I hope this information might be helpful to others.