My wife and I have eaten natto beans on and off, for over a dozen years.
They are strangely slimy, but otherwise don’t have much taste, which is why they give you both a vinegar and a mustard packet.
They are the highest source of vitamin K2-MK7 in the world.
May I ask: WHY do you eat them, if they are slimy and don’t have much taste?
Maybe the K2 has something to do it.