What are the pros/cons of ram air turbines?
You have kind of answered your own question. The down side to ram air turbines is they cause drag.

The up side is that they provide power outside the internal generating capacity of the aircraft (e.g., in emergencies when there is no power).

In the case a of a jamming pod, having its own power source eliminates/reduces the need to rely on internal power. That makes the pod modular. If the pod did not generate its own power, there would need to be a generator inside that sits there regardless of whether the pod were attached.