Anything I could comprehend at double speed would probably not be worth listening to.

A few weeks ago I listened to Dawkins's audio reading of Darwin's Origin of Species at double speed.

The simple fact that many people read at double or more speed compared to speech suggests that doubling the speed need not reduce comprehension at all.

There is an optimum speed for comprehension, and for me it seems to be closer to double speed for something like the Origin of Species. To see that slower is not always better, take it to an extreme to make the effect obvious even in imagination. Suppose the audio is at 1/4 speed. At the end of a long sentence, you may have trouble remembering how it started.

If I fail to understand something to my satisfaction or my mind has wandered, I use the "jump back 30 seconds" button once or a few times. Another useful feature.

If you try double speed, at first it is likely to seem overwhelming. But give it a chance. After I have listened to a book at double speed for a long time I find that standard speed tries my patience.