There's a TON of power generation alternatives that look much better both from the "trying to not give you a lot of cancer" standpoint and the "efficiency is something we care about" standpoint. Most RTGs make about 3 to 6% efficiency, while a random Amazon 100w solar panel will give you 15/22% without most of the risks.

The main reason this are used vs (or sometimes along!) other technologies is that they function rather happily in super crappy conditions we don't -unless some world-ending event happens soonish- usually have on Earth.