Getting the flu shot is essential, but it's not the most fun thing to do. It takes time, it stings, and you're not guaranteed a Barbie band-aid. Since you have to get it done anyways, these stores give gift cards for flu shots, which makes the task seem slightly less onerous.
And you have to get the flu shot. I know, it's not fun, but according to the Centers for Disease Control and Prevention (CDC), tens of thousands of people die from the flu every year, and when you get the flu shot, you're not just helping to protect yourself, but you are also, hopefully, helping to protect vulnerable communities of people who cannot get the flu shot. Communities that include newborn babies and those with autoimmune disorders, or cancer patients who are receiving chemotherapy, and for whom the flu shot might not be as effective.
Yes, it is true that the flu shot isn't a guarantee. The CDC admits that from one year to the next, they're not sure how effective it will be, but it's way better than nothing, and even if you do develop the flu, having the shot might attenuate the virus... which could make all the difference. If you haven't gotten the stick yet, you might as well get a little bang for your poke, and get it done where it will most benefit your wallet.