Unfortunately, I don't think it is. I used to use knock-off toner, but after a firmware update, the printer would no longer recognize those cartridges. Luckily, I had bought them on Amazon, so I just explained the problem to customer service and got a full refund. I still love the printer though.
They kind of already did, at least they did in the past.
They fought pretty hard to make you only use their toners, and they would warn you to change your toner cartridges way earlier than it was necessary to do so, disabling the printer if you didn't. I remember having to put tape over the optical device in the printer that looks at the toner cartridge, just so I can keep using my toner cartridge.
Don't get me wrong, I love my brother mfc7840w printer, but it's so weird to hear so much praise for Brother, it's like there is group amnesia about how they used to be on some of this stuff themselves.