I just have the three apps: Podcatcher, Audiobook Player and Music Player side by side on my phone screen so don’t “forget” them.
I don’t mind an app adding non-core functionality as long as it does not undermine its competence at doing its main job by making design compromises in order to do so.
In this case I would actually welcome Play Folder as Audiobook as long as it included the same aggressive smart rewind functionality of SABP which I find so useful to regain context when listening to long radio programmes with frequent Pause/Play while working as a multi-drop driver.