Yamaha has great quality and design, and this product is an excellent example of something very useful, but also an engineering work of art. It makes fun work of connecting instruments, amps, PA, in mono and stereo, inputs and outputs, mixing, and USB to the computer. Compared to the lower price competion, it's simply built better and the design is hands down the winner. Sound is clean on guitar and vocals, and the FX works well, applied as you like to each channel. Every feature tried, and there are lots of them, has worked well.
Most musicians will want the USB of the XU and the faders, a good break from all the knob twiting you'll be doing. So the MG12 XU is the minimum you'll want, and likely all you'll need. Perhaps a 16 or 20 for a larger band, but for 1-4 members, it should do the trick. It works well in the studio and on the road. Rugged and portable, you'll want a travel case and some larger laptop cases will work fine. Just pad the knobs and faders, and you're off and running.
I only knocked a star off the features because of the bundled software, an outdated version of Cubase. It takes too much time to use, and while professional, it's a limited feature version, and it's AI interface is decades old. There are many better, easier to use products out there, for example Garage Band on the Mac is much easier and faster to use, and you're not handicapped by installing it on only one PC. Most touring musicians will want a desktop for recording at home/ studio, and a laptop for the road. Can't use Cubase then. I sent a simple message to Steinberg product support, and it was 2-3 weeks before they responded with a non helpful answer.
But sticking to the Yamaha hardware, it's fantastic. Perhaps Yamaha will catch on and supply their own software. Just don't buy it for Cubase. Happy mixing!