the one thing that works about the flag is that it's made of fiberglass (or some other similarly solid synthetic), which makes it stiff enough to stand upright, but flex enough to bend in the wind or when it hits low hanging branches, etc. you probably could find some replacement rod material and make your own. and you're right---that flag with writing all over it is unnecessary promotion; isn't it enough that we've just forked over the cash?
i personally think the flag is mostly useless. in low light it's impossible to see, in daylight it's too small to be really useful on streets. i've found that mounting multiple good-quality blinking red LEDs on the rear is much better for safety. good LEDs are still noticeable in the daylight, and very (very!) noticeable in low light. sure batteries are required, but it's a small price to pay for being noticed. to that effect, avoid the cheap LEDs (low power LED light, poor lenses, poor strobing), and make sure the batteries are always strong enough to produce the required amount of light.
of course, two quality LEDs will cost you about $40, which is more than an OEM flag. but hey, it's safety, right? would you mount a flag on your car if your tail light burned out?