It should work fine. 5V, 300mA is pretty standard for many portable devices and a good fit for the 400mA battery of an M6. The 700mA battery of the M3 would take longer, but would also work.
I got an opportunity to try it and the Teclast AC Wall charger will not work with Meizu M6.
Probably difference in polarity assignment. I recall having the same situation during the Portable CD player days with Panasonic and Sony. Though both have similar voltage ratings, you cannot use the charger from Pana to Sony because of different polarity.