After changing the black toner cartridge the first several pages printed were half solid black. I don't know why and it scared me. Fortunately and without reason that stopped. Pages are printing properly now but I am still nervous.
I’ve used HP ink and toner for many years. Wish the cost was lower. It has not been a problem installing new cartridges. The old ones you can recycle for free - just put in the box and attach the label they provide. Drop at UPS or leave out for pick up.