It is absolutely frictionless and cheaper than competing services.
All my titles are available on all my devices, and progress syncs perfectly.
As a consumer, it is far far easier and more convenient than having to manually download mp3s off a shared drive or something, never mind the issue of how you sync progress.
It doesn't abuse me. It makes my life net better than it was before I used it.
This is a really important point for you - many people value what they practically get from a service - not abstract concepts of freedom.
What I care about is getting to listen to the book. I don't care about your DRM problems. I don't care about file formats. I care about the words that the author wrote going into my head. That's what I came for. If they give me that I'm a happy customer.