According to folks at SamMobile, who have been using this firmware for quite some time, the updated version is faster and brings Knox security service and Samsung Wallet app to the Galaxy S4. The company also seems to have included a Reading Mode, which optimises the display for reading the textual content.
In addition, the stock Samsung keyboard has been improved and there are a few UI changes. Apart from this, other changes are under the hood and improve the overall experience of the device.
The adventurous users can grab this test firmware to flash on their Galaxy S4 smartphone from the source. Here is a video of the updated Galaxy S4 in action.
