I've used the MidJay on a 5-hour performance last Sunday without a problem!
Here's my first evaluations:
1) It's so easy to use & set up when you get familiar navigating with it.
2) The styles & sounds are very realistic & outstanding. It's totally compatible w/ Ketron's SD1, X-series & som GEM's styles. I bought a USB style cd w/c contains 1000's of style from different k/bs.
3) It's so compact that one previous owner of a dance hall commented that he can't believe i can do realtime arranging, plays SMF, wave, MP3 & audio effects on this device.
4) PC friendly thru it's usb & treated like another hard-drive.
5) Has stereo line in w/c is very useful when you need a sub-mixer or another device in my case multi-format cd/karaoke player.

As with very new device, MJ has it's glitches & hiccups:
1) Registrations can only capture styles, tempo, transposition & voices but not intros, & variations.
2) You cannot overwrite existing registration as it will be corrupted.
3) I have 3x experienced half-screen blank outs but never happened again.
4) There were couple or more midi files that when i played the MJ would freezed.

They said that MJ was designed primarily as a multi-format media player & second as an arranger, but in my case i'm happy & satisfied with it's arranger functions. Now i can take this machine everywhere i want to go. BTW, i'm using this w/ an Evolution 61-key midi-controller keyboard.

AJ of Ketron is working on the next OS that addresses these issues.
I'm also waiting for the vocal harmonizer module to complete my ultra-compact system.
AJ, i'm eagerly waiting for the these improvements.

This compact machine is a definitely a keeper & perfect for my application!
Jimmy