Pros: Superb sound quality in all aspects; Long battery life; Plenty of power; Option to disable USB charging; Very good DAC; SPDIF in both ways
Cons: Heavy; Easy to accidentally turn volume control; Recessed USB socket causing cables to fall out, GSM noise susceptibility in OPA209 version; DAC limited to max. 48k/16bit via USB
This review describes version with OPA209, but other ones should perform on par or better and probably without GSM noise issue.
The amplifier is powerful enough to drive power hungry headphones such as orthodynamics, but also has very low impedance for balanced armature IEMs.
DAC, while very good, is not the absolute benchmark - but that is to be expected in an integrated device. Opamps can be replaced - they're SO-8 mono versions attached via a DIP-8 adapter.
The only actual drawbacks of this amp are related to ergonomics. Especially the very sensitive potentiometer can be problematic.