Battery life
To be honest, the important thing is that it's more than 24 hours - which means that the charger is on the bedside table, next to the smarrtphone charger. When you have a wear-all-day device that runs out in less than a day (Glass?) then you have a major useability problem.
Still can't really see why most normal people would want one though.
Biting the hand that feeds IT
