I quite like the idea, anyone who has tried to dig the right amount out of a jar which has been kept in the fridge will know this. If it is on cooled toast it drags the butter/margarine off the bread and onto the knife with it, and you have to try and force the resulting khaki slurry off the knife, back onto the toast without the toast disintegrating.
If it on hot toast the melted butter provides a skid pan for the Marmite on the knife, and you end up squeegeeing the butter off the toast, while the marmite remains impervious to the toast.
In short marmite is like a child that doesn't want to go to school, and hangs on to the parent with more arms and legs than they had when you left home that morning.
It's a bit like trying to get rid of a chewy bogey, using a toothpick.
Giok