the stone itself goes for $70+ and the half mask goes for $20+
the stone is coarser (180/600) combo than the more popular 300/1000 (FC) combo.
even though made in china, stone is supposedly high quality (monocrystalline, electroplated)
the mask seems to be rated well. it is made in UK.
there seems to be rikon version that seems to be very similar.
do your own diligence but seems like a good deal.
i got one set.