I thought I had read it in an article in Photo Techniques several years ago, but now I can't find it.
I am pretty sure it was Brett, but I may be confusing it with someone else. Perhaps Michael Smith can clarify when he gets a chance.
I have not used one and your mention of it was the only other time I have heard of the device.
I have used spottone on occaision in experiments but have yet to get consistent results. Usually I use a very dilute solution and build up the density of the area, but I have not done enough to be able to make a good estimate of the effect when printing.