The only downside is I have to make sure I pick my audiobooks carefully. Ideally it's things that I want to listen to in the car on long drives, but wouldn't read day-to-day, and so end up wasting the extra $10-15 narration.
I've been using Rockbox for more than 10 years and know the interface by heart (there was one occasion where the screen broke on a player but I could still use it perfectly fine, by counting the button presses) so one part is just simple habit.
There is no personal information on the device, so there is no need to lock it and for me to try and unlock it in a hurry and if I lose it it's only annoying.
I really like the physical buttons, I don't have to look at the thing to do stuff (yes, there are other solutions to this).
Battery life is usually excellent.
At the moment I'm using a SanDisk Sansa Clip Zip. Once that thing breaks I'll probably just use my streaming server (via airsonic) on my phone and yell at the touchscreen because I have no idea what dedicated player is still usable with rockbox (apart from the refurbished old ones).