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.
We run third-party toner in all of them, and they'll keep printing until the print quality fades.
I personally haven't tried refilling toner cartridges in a long time, it's not worth it when third-party toner cartridges are as cheap as they are and the Comprenew up the road takes the empty ones back for recycling.
At work, we have an MFC-8950DW laser printer and it's not very good. It leaves streaks on the paper and the toner doesn't seem to fix properly all the time. I end up with printed pages that smear or the type rubs off. That printer replaced a much older Brother laser and it was better. We "upgraded" simply because drivers were not available for 64-bit Windows.