You get a decent bundle with the Ray DA-P1 DAC / Amp. There is unfortunately no compact OTG cable in the bundle. Given their scarcity online, it would have been a great feature to bundle with the device. You simply get a normal USB to mini-USB cable, which will not allow for a direct connection to an Android device, but the carrying case is big enough to both fit the DA-P1 and a set of earphones. There is also a charger, a mini-jack to mini-jack cable, and an Apple LOD to mini-jack cable.
The unit is very well built. Its case is made out of aluminium. Both the dial and jacks seem to be integrated well, which is essential for a device that is for use on the go.
The front has both the input for the headphone amplifier section and the headphone out. Moving the volume control or plugging jacks in and out is never difficult due to space limitations, and the device is small.
The backside of the DA-P1 features the USB input. The unit is also charged over USB. Layout-wise, this little amplifier is very well off.
Even though the O2+ODAC is small, its compactness is not even in the same ballpark when compared to the DA-P1. The size is right at the limit for not being a hassle on the move.