I had before the FiiO E12 but the nano iCAN wins easy.
+ additional X-Bass is much more punchy than the Bass implementation from the FiiO E12
+ additional 3D sound is more realistic as the crossfeed implementation from the FiiO E12
+ the battery life is (depending from the cans) 2 to 3 times longer as from the FiiO E12
+ the nano iCAN is powerful enough to drive the HD800 which is the biggest can I use
only con side, the nano iCAN is a little bit more expensive and need the separate (included) 9V charging kit from iFi to charge the battery.
I compared both too, and sold the iCAN.
I do not care about special effects (mega-bass and corss-feed), so those were not even checked.
Battery life, I trust the manufacturer specs, as for me, I never reached the oh-no-I-need-to-recharge moment in the middle of a listening session.
The 10+h of the E12 are more than enough for me.
The E12 is quite a bit smaller, *and*, re-charge from USB, which is a big plus for me.
The E12 has much more power, with its 19v peak-to-peak output.
The iCAN is powerful enough for my listening habits too.
Sound wise, I prefer the E12 WRT the iCAN. I notice I tend to get fatigued after some time, with the iCAN, thing which does not happen with the E12.
The iCAN has a pop on the HP, which the E12 does not have.