Also a satisfied Brother laser printer user. I have the unit blocked in my router so it can't surreptitiously update its firmware and start doing this.

I always buy the Brother toner cartridges because they're the best quality, reasonably priced, and I want to support the business model of the only(?) decent printer manufacturer left.

All of this said, if I found out the printer was locking out third-party toner cartridges, I'd stop at nothing to defeat the lock, and would only use knockoff toner from then on.

It's an honor system through and through, I hope somebody in charge takes note.