Works with the USB-RTS01 cable as well as the RT-42.  

Things to consider:  

RTS-01 plugs into the CIV port.  There are two ports on the back of the radio that are 3.5mm.  Good chance for error.  The CIV port is the one on the inside nearest the USB-B port (where the RT-42 would plug in). 

Advantage to RTS-01 over RT-42 is the drivers.  If you have several devices using SiliconLab drivers, the program could get confused about which it needs to address.  Suddenly you are having to unplug other things to get programming for one radio... There is  ForceSerialPort (see knowledge base article) that will let you hard code the com port designation for a given radio. 

The RTS-01 forms its own id that the programmer can find without having to unplug other SiliconLab devices and without having to manually set com ports.