1) The Focusrite is 24 bit, the mixer is 16 bit
2) My experience with less-expensive USB mixers (not just Behringer, I have a Mackie) is that the A-D converters are noisy - a high-pitched whine that is only controllable by keeping the USB output low. As the Behr mixer does not have a separate USB volume control, the volume on it can only be controlled by the main output volume control.
mixers are for mixing. audio interfaces are for recording
