The Spotify® ads are not part of the episode, it launches a new file basically and you get a new seek bar that says 30 seconds total rather than it being part of the audio stream that you downloaded. I was frankly surprised it let me seek to the end, but yeah that's not gonna last long.
Also, I'm a premium member and I got ads on a podcast (from one of the ones they own themselves no less!). Fuck that shit. Unsubscribed from that podcast and will also from any others when I hear they're now "exclusive". I don't need more ads for products that I already paid for in my life. I also keep considering reverting to the pirate bay and a €13 128GB sd card, since the player is rather buggy and I can see in my firewall that the app tries to report who-knows-what to Facebook and other advertisers (again, as a premium member...), but it's not Spotify that would hurt the most from that so I feel like there isn't really a point.