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.
#1 is a simple setting in admin console of the printer -- at least for my model.
It is called "replace toner" = "continue".
Default setting is "replace toner" = "stop printing".
I print for MONTHS at a time after the printer displays "replace toner" message with perfectly dark prints. Even when the print starts to fade out -- this setting ensures the printer wont refuse to print. Just keeps showing the low toner warning.
#2
I have not come across this restriction myself. Happily using cheap third party toners bought off Amazon for about 6 years now.
#3
Did not try but my guess is that should work too. I was just not motivated enough to try because cheap $10 toners on Amazon do the job for me.