My company looked at them, and we were very impressed with the product. The only issue was that they are built for general compute and we really needed the option for faster processors.
I love the typescript definitions! I do have to say the way that pasting anything into the URL bar deletes the existing URL is super painful! I just wanted to change the variable case :(
The fact that you also have typescript defs for the URL parameters is a nice touch though.
The Natrium data sheet[1] says that it is "Molten salt energy storage", so based on the diagram[2] it appears that salt (not sodium) is being pumped to to the reactor and stored in large tanks, similar to thermal mass solar installations. I assume the sodium is internal to the reactor only, but can't say for sure.