Ah I see.
Maybe I am a bit biased as I have had the Fiscon from the first weekend of owning the car but if there were functions I was clearly missing I'm sure I would have realised that by now, 3 months on.
Ok here are my thoughts on the Fiscon.
The phone button on the steering wheel doesn't work. What function does this serve when working? I can answer and terminate calls using the OK button.
I can operate all the functions using this button but why would I want to go through a dozen key presses when I can select the same function on the headset with only a few key presses?
I can see the DTMF tones certainly being an added advantage. However strangely enough I've never needed this option in the 3 months and only tested it out when it was mentioned on another thread. I only ever call my wife or kids while driving and they are all programmed into the front screen of the RCD510. For those that make outgoing calls to companies and their mailboxes, I can see this is a must though for the DTMF.
One thing I would say though is the £100 or £126 fitting fee is an absolute rip off. It is childs play. Literally a 5 - 10 minute job. Fair enough the VAG COM may present you with problems but I'd rather give an independent £20 for a couple of minutes work. Or do like I did and gave my salesman a bottle for getting it done for me picking the car up.

The unit looks identical to the Fiscon and I believe it will be, so why could Fiscon offer "free fitting" via the group buy?