I suppose that one may argue that this make it more valuable to a serious magician and a better investment as the secret is better protected.
To those that can afford this product, they're not about to spend £500 and then tell everyone how they did it and I suppose to a serious and working magician (=Pro), it's likely to be considered a good spend when you can claim the cost against tax.
You have to admit that you'e have some serious fun with a bottle like that

More frying than a chippie at Friday tea time

Member of the Magic Circle & The 2009 British Isles Close-Up Magician of the Year
It's not really an optical illusion - it just looks like one!