When I started writing my first-ever iOS app (coming from web dev) the only thing I knew about App Store subscriptions was that they were annoying and hard to get right. Being a noob to iOS, Swift, and the App Store I was not looking forward to figuring it out myself.
Fortunately these guys were launching at the same time we were and offered to let us into the beta. Dropping in the SDK saved me literally months of stumbling around in the dark trying to do it myself, poorly.
Support has been top notch and they're building out new features constantly.