I've used it a bit, and it's interesting stuff. I usually use it at the instruction recommended dilution, cut the agitation to once every 5 minutes and stretch the time out to compensate. I have not put the negs on a densitometer, but I'd say the claim that it increases film speed is accurate to some degree. The resulting negatives are very, very sharp, and edge effects are greatly enhanced. Depending on the scene and lighting, it can drag every bit of detail out of a negative.
The downside? It can produce negatives that make prints look a little harsh and gritty. With some films, notably Ilford PanF Plus, it can produce exaggerated edge effects that, to my eye, are too much. If I was to use that combination again, I would opt for a more normal on-the-minute or half-minute agitation scheme to cut back on the edge effects.
I've had the most success with TFX-2 and Agfa APX-100 and Fuji Acros. I'll be experimenting more with it in the future as I now have access to a good darkroom. You might search this forum for posts on this developer by D.F. Cardwell. It is a developer well worth trying.
Peter Gomena