I've been using SW for the past year, and it's been a lifesaver. Not just for paywalls, but for emergency popups, help pages and anything else you can't wait for App Store Review for. Beautifully designed, clear editor makes making even complex paywalls easily accessible to designers and devs alike.
I built my first iOS app over these past 2 months, and Superwall made creating a paywall, dealing with user subs, and getting metrics super easy.