Conceptually, liquid metal cooled fast reactors are fantastic. Self-regulating, can be used as a breeder or burner, depending on configuration and fuel selection, and will shut themselves down in a LOCA (so no risk of meltdown, but of course sodium has other challenges). They also produce much higher temperatures that align with traditional fossil turbines, making them more thermally efficient for power production and a potential drop-in replacement at existing sites.
However, the US has VERY little experience designing and operating them, most of this experience is in Russia (the BN-600 being the most notable example) and France (Phoenix).
My position is thus hesitantly optimistic. I fully expect this project to go over time and over budget. If you look at Vogtle, the reactor design the West has the most experience with (PWR), and how much of a blowout it was on both of those fronts, it's effectively a guarantee that the same will happen here, and perhaps at an even grander scale.
That said, this isn't like fusion where it's always 10 years away. FBR's have been constructed and operated for decades, so this isn't hypothetical that it will work, there's plenty of evidence that shows that it does. The challenges will be economic operation, reliability and hazard shielding/management, which are quite different with this concept from traditional LWR's and HWR's.
