Yes I have used them, both on my Trek 670 and later on my Jan de Reus
(before putting on CdA deltas).

I didn't like the noise, they seemed to squeal as badly as Mafac racers if not
properly adjusted. They didn't stop any better or worse than most of the brakes
of that particular era. I believe that was more to do with single vs dual pivot vs center pull design
than the shoe material.
Anecdotal evidence suggests that sinterized pads were harsh on hard anodized
rims. I've never experienced this personally but the "legend" had to start somewhere.
I seem to recall that the sinterizing material was asbestos, at least originally, however
I can neither confirm nor deny that.
Bought mine from Banana Brain on ebay.
Marty