Okay so here is what has been explained to me.
The promo code: bgcaps can be used a total of 60 times, but only 10 times per day.
Therefore: 10 people each day for 6 days can get this key cap for completely free (includes shipping). So why not? I used one of the codes so that leaves 59 left.
I was told this was specifically done for GeekHack and its members.
If you do use one of the codes try and post back here so we can have an idea on how many are left.

The link below will take your straight to the items page. Just add to cart and enter your promo code and select the free shipping method and you are done.
Thanks,
http://www.banggood.com/R4-Or-ESC-Height-Supreme-Pole-Pattern-Replace-Personality-PBT-Keycaps-p-83909.html