Diamonds are so special because they are rare, unique, and cannot be made by man. Anything that can be mass-produced might cost less, but it's also worth less, and after a while, worthless.
To prove it, he is giving away a FREE 1 carat lab grown diamond when you buy a Real Earth Born Diamond™ Engagement Ring from Steven Singer Jewelers. And in a few years, your free diamond will be exactly what you paid for it, nothing.