I have an Artiphon Orba midi controller. You can use Orba using MIDI over Bluetooth on macOS, iOS, and Android. It's small and super portable. It is like new and barely used. 

"Orba is a handheld synth, looper, and MIDI controller that lets anyone make music immediately. With Orba’s integrated looper you can layer Drum, Bass, Chord, and Lead parts to create beats and songs on the fly. Play through the built-in speaker or use the ⅛” jack to connect headphones or amplifiers. Pair wirelessly to the Orba app to customize your instrument and share your creations with friends."

100,000 won

Preferred pickup near Gangnam