I'm a radio reporter and bought this to record directly to my iPad, iPhone, or even laptop during press conferences and interviews.
I have a M-Box that sits on a desk and does this nicely, but wanted something that could natively work with my mobile device and was more portable. I would have bought the iRig Pro, however that doesn't allow for monitoring your recording, so I went with the Rig Duo.
The audio quality was great! The device met my first criteria -- it could connect directly to my phone and tablet without any adapters. I was able to record and monitor audio levels while doing so using a wide variety of apps, which was great. You would think this would be headed for a five star rating, but you would be wrong.
My second criteria was portability and on that front it failed miserably. It was too big to fit comfortably n my hand (even bulkier than my Zoom H5). The device also had a concave contour and was slippery, both of which added to my difficulty in holding it.
It was incredibly lightweight, but not in a good way. The plastic felt cheap, as if one drop and my $200 was down the toilet. For someone who uses this day in and day out, often in less than ideal environments this simply was not going work for me and so I sent it back.
That isn't to say that it might not be a good fit for a musician who just wants to plug a guitar and vocals into an iPad or something like that, but the advertised concept of "throw it in a bag and take it with you" doesn't work. Therefore, while I'm writing that I wouldn't recommend it to a friend, the real answer is that it would depend on the friend's needs.