Nice review!

Spot on the ak10 IMO gives a big step up for most android devices, as most android devices simply do not have as refined dac and amp stages as the iphone. As for the iphone, you are right that it controls the phone volume slider, im not sure whih stage the volume control is implemented, but i believe it was deliberately made like this to give flexibility in volume control. Sonically, i also feel that the differences were subtle at best sonically, and more in terms of volume control. You are absolutely right there many people just dont realise just how well implemented the dac stage of the iphone is

almost a reproduction of iriver AK10

Nice review, I got one used pretty cheap and I'm happy with it a laptop DAC/AMP.

Yep - overall I was happy enough with the unit to actually buy it from Beyerdynamic, and that should be endorsement enough.  I still can't get over how good it sounds for such a small footprint.  Mine lives mostly at work now - it's brilliant.

Footprint aside, does it justify the price tag? How does it compare to a Fiio E07k for example?

I haven't heard the Fiio E07K - sorry.  I got mine a little cheaper than the RRP.  Value will be different for each individual.  For me it's pocket sized, portable, has a very good dac, and a reasonable amp with very good volume control - and compatible with iOS devices.  So it really ticks all my boxes for my personal uses.  For full price ($299) I'd have to think about it - but if you can pick one up used for about 2/3 of the RRP, then I'd consider it a pretty good deal.  I really like mine and use it every day at work.

Oh - forgot to add - I did end up buying one.

Thing is, $299 means 299 euros ($400) here RRP. It;s a niche product so chances of finding a used one are slim to none

I actually like the volume control dial in the form of a turn table.  I like that a slip of the hand will not blow out my ears and that it takes several revolutions to make a serious increase in volume.  
This is January 2016, so the price has come down from the initial release but it is doing a nice job with my iPhone 6, and Macbook Air (2012).  The leather case is an important extra that if the amp drops, it provides nice protection.  

Over here it's still firmly stuck at 299 euros.(325 USD)