This range was discussed not long ago when it first came to Q and as I said then, they are identical to diamonds - more importantly, they TEST as diamonds.
An unscrupulous jeweller could buy it off you then sell it on re-mounted in a different ring.
The visual difference between CZ stones and natural or lab-grown is obvious. To find a natural diamond as white and without inclusions as Eek would be very rare and very costly. At first glance, the lab-growns will pass to any jeweller as natural so if you want a real diamond at half the price (at least) of the real thing this could be a consideration.
They're also conflict-free which is a big plus.
The jewellery trade is rife with modified natural stones that are filled and heat-treated but sold as higher grades. Even worse are the High Street chains that will sell low-grade diamonds of poor colour and so included they look speckled grey (that you will definitely NEVER get back anywhere near what you paid - which in the chains' case will be massively over-priced). I don't mind the look of some of these 'speckled' diamonds but I hate that they're sold as 'the best' to people who don't know better.
I have a beautiful 2ct+ antique cut diamond that I've been told to send for re-cutting into a modern brilliant and sell. Neither of which I'll be doing as it's very sentimental (mum's that I had re-set) and I prefer the cut to the moderns. If anyone is interested Google OEC diamonds, particularly jewelsbygrace.com or have a look at the August Vintage cut stones on goodoldgold.com (I was also lucky enough to have inherited a lovely old cushion cut - lucky in that I still have them because had they not been in my purse ready for re-sizing, my ex would have taken those as well as my nan's engagement ring and other family heirlooms).
If I wanted a bigger stone but couldn't afford a diamond I'd go for one of these with no hesitation. The 2ct is cheaper than a 1ct of similar spec at a high-end jeweller in my nearest city. I reckon I'd get near the same price for either if I sold them second-hand but will have had a really nice bigger stone (2ct looks better on my hand than 1ct - though some people do look better with smaller stones) to wear in the meantime.
Then there's the insurance aspect. A lot of people are uncomfortable wearing expensive jewellery out or can't afford to insure it. So they end up leaving it in the safe and wearing CZ instead.
If, as in my case, the marriage fails and the arsehole demands the ring back it won't sting as much to return something you know he wouldn't get back quite as much had it been the real thing. If, as I did, you get the 'demand' letter for your engagement ring AFTER the divorce is done and dusted, do as I did and return a similar CZ instead (and then sell it yourself). I later heard that he was a bit angry - hopping bloody mad apparently - when he took it to sell and was told it was worthless. (He looks like Yosemite Sam, too
)
And there's the absolute joy with CZ. They look convincing enough to someone without experience but don't cost a lot.