I just purchased the Zoom U-24. I love it because it can run off battery power and has a great selection of inputs and outputs right on the unit. And it's super affordable. Got one during Christmas for $125 brand new. I strapped a 15000ma USB battery to it with a zip tie and it's a totally mobile high powered interface. There is lots of more expensive stuff out there that can run off bus power, but lots of those solutions like the appogee ones also require breakout cables to connect. The zoom is great because everything you need is right there. You can also use AA batteries, but apparently those last 3-4 hours. With the rechargeable USB power I have it can go all day.