I don't know anything about the FLARM LX Redbox.
The chipset converts RS232 signal into one that the PAW or PC can use via a USB port by creating a software coms port. FLARM devices use a 9 pin D connector, RJ12 or RJ45 depending hardware to output the FLARM signal from it's inbuilt RS232 chipset.
You can connect a FLARM device directly to a PC that has a Hardware Coms port (9pin D), or Via a lead like I linked to above. Hardware Coms ports are getting rare these days, and very unlikely to be found on a newish laptop, hence the need for a USB version.