I got this for my brother, so these are his thoughts on the device:
"I got the i2M to explore the world of synthesizers with my guitar. I'm a lousy keyboard player, could not afford a proper guitar synth so I decided to give this little midi buddy a try.
The thing worked right out of box on my Mac with both Garage Band and Logic 9. However, it certainly helps to a) download the software (free), b) download the latest firmware from the Sonuus website.
i2M is monophonic so don't expect to play chords. However, you can 'multiply' the tone using the Sonuus utility and create octave or key-based harmonies.
Depending on the setting, the i2M supports string bends, however with that feature disabled (in the chromatic mode), the tracking improves significantly.
Tracking accuracy depends on several things:
a) your playing style - the cleaner you play, the better tracking you get
b) volume of your guitar / sensitivity settings on i2m (essentially, make sure your guitar is not set to 11).
c) synth sound/setting - fast attack sounds work better for shredding. In other words, french horn is not an ideal sound if you want to play van Halen's Eruption.
The great thing is that i2M works both as a midi converter AND audio interface. At the same time. So yes, you CAN play that great distorted guitar solo with the sound of a Hammond. Or anything you like.
I found this very useful when traveling - essentially, you only need this little thing (chewing-gum sized) and your laptop to fully use whatever software instruments and guitar emulators you have installed.
If you're a guitarist and/or songwriter and want to record guitar and lay basic tracks for bass and synths wherever you are, i2M can prove extremely useful and versatile.
Sure, it's only monophonic but you still end up with a midi track that you can use and process as any other midi."
This is the test my brother wrote for a Czech music mag Muzikus:
http://www.muzikus.cz/pro-muzikanty-testy/Sonuus-i2M-musicport-MIDI-prevodnik-a-vysokoimpedancni-audio-USB-rozhrani~06~brezen~2014/
