It just sounds scary but like most Russian things its a piece of shite.
It's a very expensive and hard to make missile to use against Ukraine when they have plenty of other cheaper ones that do just as good of a job. Using it on another country like the US would just trigger a massive war and possibly a Nuclear one and you would need thousands of those to make a small dent which are expensive and hard to make so why not just use Nukes. Now nuclear powered nuclear missiles would be pretty damaging since they would be harder to intercept but still, mutually assured destruction just one side would have faster missiles. Not going to stop the MAD. Using them with naval engagements would make more sense but as we have seen with the Ukraine war Russia does not really have a good record of successful missile launches with a lot of the regular conventional ones coming back down on the Russian populace. Cant see a more complex one having that much better of a record and while the Russian populace will take a bunch, spewing nuclear material into them might just be too much. Its a stupid idea and just another "look at the scary thing" from them.