All4Cellular's Daily Deal page has the deal, including a countdown timer. The deal is good for only one day. Free shipping is included.
It is reportedly not a knock-off, but instead an official cable. Meanwhile, pricing at Apple's online web store shows the cable at $19, with $4 shipping, meaning the deal cuts the price by nearly one-third.
In addition, Apple's online store charges sales tax. It doesn't appear that All4Cellular does, at least not to California residents.
Apple's Lightning connection change was reviled by many. Although Apple provided adapter solutions, which allow end users to use an old cable with the new connector, those adapters wouldn't work with docks. The new connector meant, therefore a few things which cynics immediately saw.
a) added expense to third-party dock manufacturers to support the new connector
b) (on the other hand) added sales to third-party dock dock manufacturers because of the new connector
c) More landfill
Apple could have chosen to simply use the microSD connector that most other manufacturers use, but decided against it. While some might scratch their head, the reason is obvious: proprietary means Apple gets cash added to the bottom line.
The choice of microSD could have meant that consumers had plenty of spare cables around. The choice of Lightning went against that.
One nice feature of Lightning is that the cable can be inserted in either direction in a slot. There is no "backwards."
It's true, though, that the choice of a new connector, period, was not made just so Apple could create another proprietary standard. Instead, it's assumed that Apple made the change as the new Lightning connector -- which uses only eight pins rather than thirty -- takes up a lot less space (both internally and externally).
This means that Apple has additional internal space for other components, which it can then squeeze into the tightly packed iPhone.
The Lightning connector was first introduced in the iPhone 5. It was then added to a slightly changed (only) iPad 4, and made the connector for the iPad mini.
Apple will launch the iPhone 5C and iPhone 5S on Friday, Sept. 20 -- in terms of a retail launch, that is. The iPhone 5C went on pre-sale on Friday, Sept. 30. The iPhone 5S will have no presale before its retail launch.