I completely forgot about this little challenge. But, I remembered it about an hour ago. I finally tried it. I tried it on plain white toast with a layer of butter, and another toast with a generous spread of peanut butter. I used maybe a quarter teaspoon of Marmite.
Toast with butter -- almost spit it out, but made myself chew it up and swallow it. Nuff' said about that.
Toast with peanut butter -- tolerable. Not something I'll ever get a craving for, but I didn't feel an "urge to purge" it.
By the way, it was not the excessive saltiness that was the biggest turn-off, although that was not helping. There was something else that I can't put my finger... er, tastebuds on. I'm guessing that yeast was involved.
Now I can at least say that I've tried it. Was it the worst thing I've ever eaten? No, not by a long shot. Will I ever eat it again? No.
Now, I can imagine it might work as an ingredient in something, but I have no idea what. I'll never know, because it is heading for the "bin."
CD
I've never seen anyone pair it with peanut butter, but can't say I've peered into that many kitchens across the UK at breakfast time...