I have been toying around with two of their toning kits some years ago, the sepia and the blue ones, and had decent results with Ilford Multigrade papers. They last long-ish and are easy to control. I was at a university darkroom back then, and everybody saw them only as 'a fun thing to do'.
I've also had the bigger, full kit of dyes/toners and did a couple of experiments with FB paper [can't recall which type/brand] but they all failed; I could not get uniformity on the prints. I was thinking of grabbing another full kit these days and taking the whole thing seriously.
-Sino.