If this thing isn't even going to be based on cesium, then comparing its size and expense to a standards-agency fountain clock is a bit unfair. Rubidium oscillator modules are common and cheap (cell phone base stations tend to be equipped with them) and pretty small (Symmetricom's smallest module is I think about 2" square).

Anyway, I'm curious how well the frequency stability of this thing can compare to tube-based atomic clocks.