1 - They count pages printed and will simply stop printing when they've determined you've printed enough even if you still have toner in your cartridge.
2 - They will not work with third party toner cartridges.
3 - They won't let you refill your own toner cartridge.
So you are forced in to buying Brother's toner, and and forced to do so before you may actually want/need to.
Because I'll chime in with everyone else -- my HL-2270DW has been going strong for a decade and I've only ever used third party replacement cartridges. And it'll give me a "toner low" warning but still keeps printing.