Yeah, like what Gibbo says. In simple speak, the ground kit ensures that the difference between +12V and ground is maintained without any increase in resistance from stock grounding design (which results in +11V or lower instead).
The condenser ensures that voltage spikes (increase or decrease) are smoothened so that you get consistent +12V and ground difference.
So one is for improving +12V and ground, and the other is for making it consistent +12V and ground (the Buddy Club does both).

I want to purchase the Buddy Club condenser too because it pisses me off when my headlight dims when the AC compressor turns on.