It's a nice option to try audible books, however, I was charged before the full month was up for a Gold plan which was $16 per month. When I contacted Amazon, they refunded it. However, you may want to cancel 2 days before your month is up in order to avoid the hassle.
Also, they recommend options that I didn't know where available when I cancelled in the cancellation process: 7.95 for 3 months, and a 9.95 year light reading plan without accumulating credits. You may like those options, but why not offer them before in an open way?
Audible is not loud enough on the new HD7 Fire without connecting to a stereo or headphones in the car, so that was a big disappointment as I wanted to try it out and let both of us enjoy listening on the road. If you have an older car, it just isn't an option.