thanks for all the feedback
after much consideration i have decided not to buy as it look like the technology is not matured yet and i do not want to buy something that i will only use for my vacation.
i will conserve my battery to last for the day and charge at night.
For singapore usage, i already can charge my iPhone at home/at work and in my car, so no real need for an emergency battery now.
but i will go and see the usb cable at daiso in Japan.