The Duet is the best sounding audio interface i've heard for under $1000, in fact nothing else even comes close. So for sound quality it wins hands down.
However i noticed you're hoping to use it with a Macbook, and all i can say is i hope you have better luck than me. I really do want to use the duet and will keep persisting until the day i finally throw it out the window in frustration (or they release drivers that fix all the problems).
Firstly it makes your CPU increase in temperature by about 15-20º for seemingly no reason at all - all you have to do is plug it in and your CPU fan goes up to full speed. And sometimes it just disappears and becomes undetectable, even when plugged in. At this stage i'm pretty sure i've tried everything, it's just unpredictable and unreliable. If i took it with me for a job as part of my mobile rig i honestly couldn't rely on its ability to function and therefore it is completely useless to me. I'd save myself the embarrassment and take my M-Audio, which i really don't like very much but at least the bloody thing works when i plug it in.
Having just ranted on i should also mention that it may not be any fault of the Duet that i'm getting the erratic behaviour. It could be my macbook, i can't say for sure since i can't actually figure out what's going on.
Basically if you're curious i'd still say get one, and hear it for yourself it's pretty amazing. You just might get lucky with the reliability issues too. Otherwise you can come on the Apple forum and vent your frustrations on other prospective buyers.