Is a more expensive kit worth it over a $10–$20 Amazon kit?

It depends on what you're paying for. Premium kits we surveyed (SurviveX, Rhino Rescue, EVERLIT) charge mostly for the bag, organization, and bonus items like wound-closure strips, not necessarily for higher-grade medical components. Specialist communities repeatedly note that the cheapest path to a quality kit is buying a basic First Aid Only or BAND-AID kit and supplementing it with individually sourced trauma supplies.