Thought AyUp claimed to stick the electronics in the battery pack – no?
Unlike Trout and his first Ay-Up light here, I've not yet had an Ay-Up light to have a look at.
But, if there were a driver in the Ay-Up battery pack, then surely there'd be no need for the resistor, and you'd get more than one light level ?.
Judging by Trout's pictures and observations, the Ay-Up looks to be simple and very cheap to make.
Also, judging what appears to be included, or not included, in an Ay-Up, you may get 4-6 hours runtime, but the LEDs would dim during that time.
A lot of lights now use clever electronics to sustain a certain voltage to the LEDs, during the running of the light, for as long as the battery may last.