To be honest, I'm struggling to know how to get the unit to power off as pressing the power button has no effect.
I can wait for the tablet to fully discharge and then apply charge for 15 minutes or so and try the power - volume down combination which will stop the reboot after about 6 seconds, then after a blank screen and upon seeing the reboot screen I release both buttons, nothing seems to happen.
I also tried pressing the volume down on its own to get into safe mode after realeasing power and volume down, but again the device stayed in its loop.