This is another way of making a border router out of a pi. Where the AT86RF233 module exposes the transceiver to the pi and has linux running the network stack, this module has a microcontroller (NXP KW41Z) to run the network stack and talks to the pi over the UART via a SLIP link. The SWD pins are also routed to the pi for programming and debugging.
I'm running Riot on this mostly. The gnrc-border-router example is a good starting point. It sets up a SLIP interface to the pi and serves a /64 on the wireless interface and routes between them. You can also run the OpenThread firmware for frdm-kw41z without modification but I haven't done much with that.
The main relevant difference between attaching an SPI transceiver directly to linux on the pi versus adding a microcontroller that runs the network stack is that the network stacks in linux and embedded OSs like Riot are still in different states of maturity and that means that some things are only available on one platform or the other, and that the interoperability between platforms is incomplete. So if for instance you're running Riot on your end devices you may want the border router to run Riot too in some cases. Anyway that's the need I had when I made this. Also of course it's useful to have both options for development purposes.