One of the biggest reasons that 18650 batteries aren't more popular with consumers is because of their safety — if shorted or overcharged, they will burn or explode.
"Do not use batteries with damaged wraps or insulators. ... Always keep your batteries in a case when not in use. ... Never leave a battery unattended whilst charging and always be sure to remove the batteries from the charger when the charging cycle is complete. ... Recycle your batteries correctly - never throw them in the bin."