Pros
You can drive around some beautiful places. You can work independently. The pay is good for entry-level work, especially if you live in a small town. There are opportunities for advancement because it is such a large organization. The work is about as stable as you can get.
Cons
You are given too much work to do in the allotted time. Therefore rural mail carriers must resort to dangerous practices in order to get everything done in time, like driving without a seat-belt and getting out of the car while it is still running. Even the experienced carriers need to do this in order to finish within the eight hours they are paid for. On top of this, it is accepted among the workers that inevitably, in time, they will eventually need to have one or several of the following: knee surgery, back surgery, rotator cuff surgery, carpal tunnel syndrome, and tendinitis. There are probably other ailments and conditions I have not mentioned. You will feel the effects on your body immediately. You have to use your own vehicle to do this job, and it will take a serious beating. If you are on top of all maintenance issues, you may be able to preserve the life of the car, but it becomes another part of the job that you need to take care of on your off time. Even if you are lucky enough to be in a post office with a good personnel, the decisions an policies of USPS administration will make you feel that they are not on your side. If you get bitten by a dog it is your responsibility. You will be given extra work without fair compensation - if you are compensated at all.