Buy the Olaplex N°.9 Bond Protector™ Hair Serum.

It solves a problem almost everyone who uses heat tools actually has, for less money per ounce.

What was compared

1. Fixes a problem nearly everyone styling with heat has
Olaplex N°9 protects against heat up to 450°F and works on any hair type, damaged or not. Better Not Younger only helps if you are actually dealing with thinning hair, which most buyers browsing a heat serum are not.
2. Costs less per ounce, not more for less proof
Olaplex runs $10.67 per fluid ounce against $24.50 for Better Not Younger, more than double. You are paying a premium for the thinning claim, not for a better serum on the metrics both products share, like softness and frizz control.
3. A spec you can check, not a stat you can't
450°F heat protection is a testable, physical claim. Better Not Younger's 84 percent and 90 percent improvement figures come from the brand's own unpublished internal study, with no independent methodology behind them.
4. Tested and talked about far more widely
Olaplex N°9 has been reviewed and tested repeatedly across independent beauty outlets and years of use since launch. Better Not Younger sits at 382 ratings on Amazon, a much thinner track record to bet $49 on.
5. Thinning hair? Different problem, different pick
If you are 40+ and genuinely losing density, Better Not Younger's biotin and Procapil formula is a real category and worth trying for that specific issue, go for it. But that is a narrow group, not the average person choosing a hair serum, and for everyone else Olaplex is simply the more useful bottle to own.