I’m interested since it’s clear this is a passionate and talented developer, but it seems the primary feature is step tracking, which iPhone already does by default. Is Pedometer++’s step counting somehow more accurate?

Yes, the primary feature that is being marketed is step tracking, but the app in general is much more than that. It's like how flighty just is a wrapper for the flights API that you could access through Google, yet flighty is the best app for flight tracking nonetheless and is a really cool app.