I haven't had a problem with refills.
Now, there is one brand that places a computer chip on their toner cartridges, and when the cartridge goes empty, it MUST be replaced or it will NOT work because the computer chip cannot be reset. I don't remember offhand what brand it is, but I know we had one at one time. We got rid of it because we had been refilling our other one and it worked just fine with refills; and refilling was much less expensive than buying a whole new cartridge.