The app itself is actually open source. It also works on Android, iOS, and desktop/browser. It keeps all of my content synced regardless of platform. I personally like using the faster playback speed function, automatic skipping of silence, and the overall interface. Supposedly a number of features are available for free, but I bought the app when it was just one-time fee (and was grandfathered in). I personally dislike subscription.
Personally, re. google podcasts, it lacks a lot of useful features that other podcasts apps have.
I've found pocket casts to have the better set of features and functionality (for the unpaid version) compared to other podcasts apps. I don't use spotify, but it's definitely better than the recent and awful implementation of podcasts in youtube music. I tried a couple other podcast apps, most recently podcast republic, and I found podcast republic to be buggy, certain settings don't stick or work as expected.