but then if the cartridge fails it isn't necessarily going to damage the rest of the printer, as happened previously with an ink jet, and a new cartridge would restore to normal again ?
Depends how it "fails"... you might end up with a lot of toner all over the place which is a right pain to clean up fully and safely.
Just buy the original carts and be done with it. All the third party refill nonsense is just not worth the hassle.
Lasers are much cheaper to run anyway.... you shouldn't be changing your laser cartridges that often to even bother worrying about the cost of a new cart. And if you are, then you need to get a laser that takes high-cap toners.