I use a Flexcut Gold ( its in the form of a crayon, of a Mars bar size/shape) to load my strop, mainly for use with woodcarving sharps.
I think it must be something on the same lines as whats being discussed here.
It dosnt leave any noticable marks, in fact it , "rounds off" almost too well, if you aint careful and you overcook it, or, if you use a too-saggy strop.
Cant say as I know exactly what the abrasive is, its not gritty to touch...but, curiously, if you just gently wipe a carbon steel sharp, along the crayon; it instantly turns the crayon black, at the point of contact.
Got it from a Carvers shop.
Never seen one at B&Q or elsewhere.
Pity.
Ceeg