I'm currently transitioning a paid app of mine to free+subscription, and RevenueCat has made it incredibly easy to set up so I don't have to worry about managing purchases and validating them, which is allowing me to launch the update a lot faster than expected.
We're relying on RC's infrastructure to handle the subscriptions in WeatherKit. To me, RevenueCat is an extra layer of security that people can purchase subscriptions, use the app and have a good experience. That layer is invisible and it makes it incredibly easy to use & implement. If you want to build a subscription business - start with RevenueCat.
P.S. From the moment we decided to use RC, to the moment where we were confident that this works perfectly, it took us 4 hours.
We've used RevenueCat to implement our subscriptions for our Design+Code iOS app and it was a blessing for us. We saved a ton of time, resources and received valuable advice/expertise. The system takes care of all the edge cases, which is so crucial for not losing customers. Building your own in-app purchases feature is super hard to get right, so this is hugely recommended!
Dreaded switching over to In-app purchases and subscriptions because as a indie developer I did not want to setup and maintain a server to handle the purchase validation or bloat the app by bringing in the validation code on the client.
RevenueCat simplifies all that by providing an easy to use API and handling the purchase validation. This saved me time and effort of having to get up to speed on StoreKit and dealing with the differences between the testing sandbox and production.
Jacob has been helpful answering questions about RevenueCat and dealing with getting the app approved through the AppStore since there are more conditions when enabling In-app purchases.