I have used the norton plate and combo stones as a set for the last nine months.
The flattening plate has worked just fine with very little maintenance. I didn't flatten it when new. Recently I replaced it w dmt8c but that wasn't a true need.
The combo stones do everything I need for razors. I might like to switch to a different 1k stone like chosera or shapton at some point but it's not necessary
I've done knives on these a couple times but now use only for razors. Just keep them wet while sharpening and lap well before switching back to razors.
Michael