your experience with the USPS will vary depending on your location
Pros
Your experience with the USPS will greatly vary depending on which location you're assigned to work out of. Mostly good, hardworking people. Independent work usually without someone breathing over your shoulder all day. Physically demanding and motivating in general. You feel like you're a part of something important, again depending on where you are.
Cons
Some offices can be quite political. Some Post Masters, as well as management, can be very abrasive and argumentative. They can take advantage of newer employees to benefit more seasoned (or favored) employees. I regularly worked 12-hour shifts because work is not dispersed fairly. Plus, not having a set schedule and only finding out if I was working the day before. Not conducive with family life IMO.