The only issue is that the power switch no longer switches the unit off, but I’m sure it would be a cheap repair at any decent music store. i think this a good way to get one if the most sought after synthesizers ever made for a more reasonable price. In other regards operation is very good all round.
* also please note that the original OP-1 does cause a ground loop beep noise while it is plugged in, so i would recommend eirher buying the Teenage Engineering Noise Isolator - which they designed to remedy the issue with this unit.
*i have done a basic check of the battery. i charged it for a long time and just left the unit on and it stayed on for 8 hours (though i wasnt using it at the time)
*the small 1.5cm by 3cm-ish rectangular back panel isnt broken, but always falls off when the keyboard is moved