Just for clarity - Audi have not released version 660.
650 is the latest Audi release of the firmware.
660 is a hacked version of 650 that enables SDS functions.
To get the RNS-e to do a software update it needs to see a newer firmware version so has been called 660 to make the RNS-e think it is newer.
Don't forget that for SDS to work you will also need to make a small modification to the microphone wiring to make it work.
The SDS version is quite cool - being able to control the RNS-e by voice commands but it is perhaps a little gimmicky? You will need to be good at memory as there are a lot of commands to remember.
But, with the exception of some cable to make the wiring mod and a little time, it is a free upgrade so it's got to be worth doing - hasn't it?