"My XM1's single clicks occasionally results in bursts."
Firmware 1.62 addresses this issue by shortening the „mouse button down“ signal. You can use the XM1 Configuration software to flash to firmware 1.62.
"I used mousetester to plot the polling-rate and noticed that it seems to be unstable on my system."
We are working on the final release of the firmware addressing this issue. While we are working on the finishing touches, you can flash to the firmware v1.67 beta, which also includes the button release fix included in firmware 1.62. You can download the BETA firmware here: XM1 Firmware v1.67 beta.zip
Known issues with this BETA firmware are occasional mouse cursor movement to the top left corner or no mouse movement at all after bootup/wake up from sleep. In this case, unplugging and re-plugging the USB cable returns the XM1 to normal operation.
"I flashed my mouse and now it is not responding with both LEDs blinking Red."
The mouse is in boot-loader mode. Simply flashing the firmware again returns it back to normal. You can use the XM1 Configuration Software or any firmware from a download above. Make sure to unzip the firmware folder if you are flashing it without the XM1 Configuration software and run the „Endgame Gear XM1 Updater“.exe as administrator (right click in Windows Explorer -> „run as administrator“).