When I was a kid in the 80s my mother worked at a jewelry store and CZ diamonds were already considered cheap fakes at the time. The price was not comparable to the real deal because nobody was buying them at diamond prices.
They were simply dismissed as more trash belonging in the gold-plated case. It's hard to appreciate how much less informed people were back then - we're talking pre-internet. The adults around me couldn't explain scientifically what the actual difference was between a CZ and natural diamond. Just one was a fake, held little value, and was a sure way to lose your fiance.
How do CZ gemstones compare to diamond gemstones visually/in person? It looks like CZ has a lower refraction index but higher color dispersion vs. diamond, so that seems like it would still result in an attractive gemstone. The main disadvantages seem to be slightly lower refractive index (so less internal reflection and brilliance?), lower hardness (disadvantage for the gem getting scratches - possible advantage for not scratching your sapphire glass watch or smartphone camera lens?!) and higher weight.
edit: seems that moissanite (silicon carbide, perhaps unsurprisingly) is another diamond-like (though hexagonal crystals vs. cubic for diamond or CZ) gemstone that is actually harder than sapphire and less prone to fracture than diamond.
To everyone except those with a trained eye, they're virtually indistinguishable; however, because CZ isn't as hard, they tend to scratch and dull over time and thus lose their luster.
If we're talking about 'quality', CZ just doesn't compare for longevity. That said, unless you're talking about a daily-wearing-for-many-years piece of jewelry (i.e., an engagement ring), CZ is just fine for most folks, especially considering the cost difference.
I remember watching a documentary about a man who would marry (multiple) women, then steal their money and leave.
one of the victims said she had doubted the ring he gave her was real, but he just scratched a mirror with it to prove it was real. Then she said "it was only later after he left that I found cz can also scratch glass"
They were simply dismissed as more trash belonging in the gold-plated case. It's hard to appreciate how much less informed people were back then - we're talking pre-internet. The adults around me couldn't explain scientifically what the actual difference was between a CZ and natural diamond. Just one was a fake, held little value, and was a sure way to lose your fiance.