40 hours with a coin battery is impressive, but I think it is a bad decision in terms of environmental friendliness.
I suppose that's 6mA when the CPU (MCU here) is active. In idle mode that ought to be much lower (the low power monochrome display, not eInk, draws only 30µA as stated separately). Does uLisp support idle mode? Uh, apparently not automatically, but requires the user to call a SLEEP function ...