Cons are the need for an external heat source and relatively brittle porcelain. Also it can't be used in personal electronics (phones, laptops) because the running temp is too high. From an economic viability standpoint I still have weight and manufacturing cost to contend with. In it's current configuration I'm looking at $200,000 up front plus overhead to produce 1000 units per day, which is nowhere near what it needs to be, and the weight needs to be brought down by about 1/3rd, although it's already pretty low and works as-is.

So yeah, there are trade offs, but they aren't killers. Lithium is a mighty king to topple but this and a few other technologies are poised to do exactly that.