UK 2005 350 owner here. I've spent about 2000 miles with the N6 and whilst there's loads on the BMW forums using Google on this interesting HU, there's not much for the Mercy...
I have been using (even though I promised I wouldn't) my 350 for my roughly 3 hours of commuting a day, which is maybe more than most people use their car in one go, my findings so far:
I bought my N6 from Fleabay - the included wiring harness was wrong. This was (eventually) rectified by the very helpful supplier.
I was annoyed to have to cut away the locating lugs on either side of the stero mounting on the car - the N6 I received didn't have cutouts to use the lugs properly.
My Mondeo mileage hack has a £3k+ stereo I've spent about 18 months perfecting to sound just so musical, so the quality of dropping the N6 into my otherwise stock SLK isn't going to compare, but I have to say I'm really impressed with the improvement, even with stock speakers. I'm really hopeful that the unit will be up to amp / speaker upgrades.
Using - Pros
Silly amount of inputs
Reversing Cam detects steering angle from CANBUS on my car and displays it on the screen, flips to cam screen when reverse is selected and lowers audio volume with no wiring mods
Sat-Nav is very good - no lock ups, fast to locate (my GPS is stuck to the top of the glove box, under the dash) and really clear
Not bad HU amp - doesn't complain about extended periods of working very hard
Looks very 'stock'
Doesn't try to change volume with speed like the standard HU did
Integrates with the dash display and steering wheel really well
Using - Cons
Pressing the 'on' button puts the unit in standby, but doesn't stop playback? Really? Drives me nuts that I have to find something pausable, pause it and then press the off button that doesn't turn the unit off. Also when coming back to the car, the unit will not remember the pause and come back on playing. Sometimes it's nice to drive without the stereo on Dynavin?
No folder up/down control. I have 30+gb of music on SD card. With my Pioneer HU in my mileage hack, I have physical up/down folder (not track) buttons. Not having that on the Dynavin is really annoying, the touch screen isn't really safe to use when driving a jiggly car at speed, I would really prefer to have a real button to change folders. For an example, the Camero I hired on holiday last year used the rotary to select fodlers when in list view - pretty quick and much easier than dragging a scroll bar. This would be livable but...
...the HU repeats song or folder and cannot be turned off - there is no way to let the unit move from one folder to the next when that folder has been played. Pretty basic HU stuff, my Philips, JVC and Pioneer HU's have been doing this since ~2004.
On FM AF (AutoFollow) does not work. My commute is 75+ miles each way and having to manually retune is really tedious. AF is ticked and showing in the display, manually retuning (which is very fast) finds a strong signal, but AF *never* retunes.
The 'OBC' app advertised isn't present on my unit, so I can't see all the fun things that CANBUS shows.
Overall, I love the stock look, but I wouldn't spend £500 on this HU again, unless there's a BIOS update or three coming soon. It's a shame as it's a fantastic principle, just let down in too many areas. Next time, I'd prefer to lose the stock look and choose an established brand that gets the basics right.