After some three years, my wife and I now have one of these. I bought it (12 quid before discount) at Stafford in late January when I was in England for about two weeks doing some research on the Stourbridge School of Art 1850-1905. Designed as a salt cellar, but it certainly could be used for matches or toothpicks and it would be nice to know if it was ever so marketed.
The mould would be interesting, as the plunger must be vertical to move in and out, so the base of the glass item will not be at horizontal when the two-part mould is opened; the item might stay in the mould, but the turning out worker would have to look sharp.
Ours does not have the "depression" that is easily seen in Bernard's photos. I suspect that the depression is actually what we call "run down" in the glass industry. The item is still quite hot, so that area may sag a bit. Incidentally, black glass is a soft glass, retains heat, and is slower to "set up." Consequently, the glassworkers know to "go slow," and they are required to make fewer pieces (the move) in a four-hour turn than they would make using a different glass color.