when your flashing doesnt succeed try that:
keep pressing side buttons (v+ , v-, and power) all together. until it restarts when usb is connected and sp tool download clicked.
it worked for me

one another thing : this a must
+ first of all before you start these drivers must be installed correctly:
MediaTek USB Port
MediaTek Preloader USB VCOM (Android)
MediaTek DA USB VCOM (Android)
use USBDeview.exe for uninstall driver . after than reinstall it. windows making mass with this drivers. or try it on another pc.
+ than try the all steps again and again.
if it doesnt flash keep pressing three side buttons at the same time and hold it untill it restarts (usb cable was pluged.). it flashed. than i succeed.

i used Kirpitch.M3Note modifed sp flash tool to flash my firmware. it has both for m and l models flyme 6 support.