I have one of those! I had to take it apart of course.
After checking the crank's short circuit current and looking up the battery capacity, I found the charging abilities of that generator appeared greatly exaggerated. Without recalling the numbers, it would have taken an excessive amount of crank time to charge the battery and at the normal power for 3 LEDs it could drain it in a pretty short time. Since LED current goes down as the battery discharges it would take a really long time to actually run the battery down entirely but the period of useful LED power is rather brief.
Still, a fun toy.
After seeing that guy on the net selling handheld green laser diodes capable of burning stuff and generally being extremely dangerous, I had the idea of adapting that hand crank to charge a battery to power it. A hand crank burning laser. Sadly, not only were they quite expensive, he quickly closed his doors after getting all sorts of "inquiries" from government agents. Since they'd just had this slew of blinded pilot reports from what may have been 5 mW greens, the internet sale of 500mW ones had them "concerned".