I read in another thread that the radiation in that dissipates in about 30 years, vastly preferable to the tens of thousands of years of nuclear fission waste. I don't know how strong the radiation is either, whether it's more or less dangerous than fission waste.

The way radioactivity works, the faster a substance decays, the more dangerous it is. Something being slightly radioactive for ten thousand years is much better than some searing-hot exotic isotope sitting around for 40.

Not really. The big issue is with long-term deterrence, not short-term. It is fairly easy to isolate something for 30/50/100/200 years. It is much harder to isolate something from future humanity with a high level of certainty for 200,000 years. Even things with low levels of radioactivity will kill you if ingested and do a lot of harm if kept near. The problem of communicating this to future humans is a big one. How do you keep future humans who may not have the level of technology we have from deciding that the magic, glowing, heating stone is a source of healing and prosperity instead of something to be avoided?