I have 7 Norton hones. Every single one of them desperately needed to be lapped before its first use. They do not come flat. They are not even close to flat. Even if they did, with use they become dished so you need to have some kind of lapping method in place.

The DMT8C is adequate for lapping but if you want to lap a barber hone, or anything else that is hard or of low grit, do yourself a favor and put a piece of coarse wet/dry sandpaper on top of the DMT plate (remember, it's a flat surface) and lap with that to save your diamonds.