Edited by TheSilverWolf at 2017-02-13 18:50

Custom roms are very important when the manufacturer doesn't release update.
For example, for M2 Note LineageOS is based on Nougat and includes last monthly security patches.
On the contrary Flyme 5 is based on Lollipop and doesn't include monthly security patches.
I don't know about Flyme 6 but I encourage Meizu devs to update Android base and listen the user suggestions.
Flyme is a very cute rom and gestures are awesome, but there are too compromises.

Meizu should unlock bootloader:
http://forum.flymeos.com/thread-29053-1-1.html