You also missed my point
I know what he was referring to, in fact all those before him had the same point.
My point is, in order to update to 5.5.1 you'll need to unblock nintendo servers, by doing that you simply risk having an auto-update of a new firmware if nintendo releases one, which would potentially patch maybe not only yellows8 browser exploit.... Especially since people want to update to 5.5.1 mostly for eshop access or to download a dlc, or for a game update.... That's basically what I meant by "safe to update" is not a wise statement to make, by doing that you're literally opening the window for nintendo to get their new firmware in your console as soon as they release it. I already said if someone knows what he's doing, and can update offline then that you can call it safe, but at the moment it's not possible.
Summary, yes 5.5.1 is still vulnerable, but updating to it online is a risky move, not 100% "safe". I'm saying this cause I've seen it happen with people a lot before.