While I can see the benefits of having a fret that is both harder and lower density than nickel-steel, quartz is quite brittle and prone to shattering. They would not last the first time the guitar is dropped; being someone who plays in bars pretty regularly, my guitars get knocked over more than occasionally. The frets will also wear out with playing, contrary to the claims of the website.
If they are actually milling frets from natural quartz crystal (the colors they appear to be offering strongly suggest this is not the case, by the way), there are natural weaknesses and internal pressures to consider. I'm curious what the cross section looks like, and how the fret is attached to the fretboard - the frets would almost have to be glued, because they would not be able to mill gripping divots onto the tang. This would mean that the frets are more likely to pop out with changes in the fretboard dimensions due to temperature and/or neck adjustment.
It would be worth checking out, but on someone else's guitar. I wouldn't blow $1500 on an experiment that is so radically untested.