there allegedly is some electronics in the ink assembly that may interfere with using non-brother branded refills, but it is possible to swap the electronics from an old toner cart into the off-brand and it will work fine. I didn't have to do it with mine.

Be aware that at least some brother lasers you have to replace another part every 10,000 sheets, which is the duration of two to five toner replacements. I am unsure if it's the heater or the laser or what.