i use many old sound cards in my retro pcs and i would have bought earlier... it helps a lot, great sound quality. the headphone is not mono of course - just the previous reviewer cannot use the mixer. very good pairing with the adam t5v.
big con to the cheaper mixers: you can set the input level well, not just mix the output.
i found smaller issues:
* the usb interface is not so sophisticated, it works well, has great sound - but the sound level looks different to the mixer levels itself. eg the playing headroom is too big - i set ~50% of the volume to a good "average" input, but at the recording i had to overdrive the inputs to get the right recording level.
* after disable the speaker output, it is not completely muted. a little bit confusing, for the headphone you got two level output volume, for the speaker just one.