Chemically and physically, lab grown diamonds are no different to natural diamonds, literally! They’re pretty much impossible to differentiate from. Generally, they’re better value as they tend to be cheaper than natural diamonds of similar size and quality. It’s mainly down to ethics as obviously lab grown diamonds are essentially built/constructed in a lab whereas natural diamond are sourced ‘unethically’ / unsustainable via mining etc.
ETA: really do not condone this ‘trend’ btw, it’s materialistic and shallow and just down right disrespectful to the partner who chose/bought the ring. But, when comes to the decision between lab vs. natural in general, it’s genuinely much of a muchness and mainly down to how environmentally friendly you are