I'm also a huge fan of the Brother printers, though I have a lot less experience with the color ones.
Regarding the toner still being filled, if you go through the web interface on most of them you'll find an option for the toner behavior: "Continue" or "Stop" with "Stop" as the default. Change it to Continue.
The other caveat I've had with at least the bigger multifunctions (anything with an LCD) is that at 100,000 pages they
all start kicking up with errors to replace the laser and PF kit. Brother says "Ship the printer to us for repair," and that ain't happening. You can actually find the parts listed in a few places, but when you add it up they're about the cost of a replacement printer, before you factor in any margin or labor. I tell people about this, and say "Basically you just use it until it dies or gets unreliable, then replace it and you'll still come out ahead on costs."
I put together something I should return to a few years ago, something looking at
TCO for various printers at various page counts. For the Brother printers I just put in the full cost of the printer as the "maintenance kit" cost, and estimated that the printers would last until ~150k pages - I've seen a couple still going at beyond 250k pages, but they were mighty creaky. I've done a few internal updates of the spreadsheet I used and I think some of the Dell printers aren't terrible, but the Brothers are still pretty close to being the winners for the areas they cover.