If you are printing anything other than normal pla, or is abrasive like glow in the dark, then this is a must. They stand up to the abuse and last. And if you switch to an all metal hotend, you will need them also for the filaments that the hotend would be able to print.

So far in my experience, the hardened steel nozzles have proven to have better prints with any filament I have used so far with the all-metal hotend. In addition, it seems like the tip won't wear down as quickly as the brass does. Can't wait to try with other filaments that I have heard work better with steel nozzles instead.