Here's what Roland say about the UM-ONE mk2
Compact, convenient, and fast, the affordable UM-ONE mk2 boasts high-performance FPT processing for low latency and tight timing. The bus-powered MIDI interface is compatible with Macs and PCs, and now with the iPad as well via the Apple Camera Connection Kit!
One-in/one-out MIDI interface with high-performance FPT processing
Compatible with Mac and Windows operating systems, and now with iOS on the iPad via the Apple Camera Connection Kit
Super-compact, affordable, and easy to use
Data indicators for both MIDI input and output
Conveniently integrated USB and MIDI cables
USB bus-powered operation