First link mentions 4*18650 batteries. That's 14 Wh. They are claiming 2-3 hours of 1800 lumen on 14 Wh of charge (250 to 380 lumen/watt). That's thoroughly implausible. Either the brightness or the life expectancy is lower. And it apparently weighs 275 g. $51 is more than what I paid for my Cygolite, which weighs 110(ish) g.