Pros
It's an enjoyable job, especially if you were stick to strictly the ARC work (package delivery). It's pretty flexible to work around other jobs, school or whatever else is on your schedule, as long as you set those boundaries in the beginning. The pay is pretty decent considering you can start with no experience in delivery. The people at my office were all very nice people and enjoyable to work with. Usually customers are happy to see you.
Cons
If you optionally do RCA Academy you'll be delivering the mail (letters and packages) probably just as much as an RCA would, except you don't get benefits. You probably won't just work for your office, especially during the holiday season. Other offices will always be wanting help. The post office is short staffed, if you go to RCA training for letter carrying then you will be called in to carry the mail for other offices as much as you are able. Which can be essentially 6 days or more a week for long days if you're up for that. I know of many carriers that have regularly worked without a day off for a very long time. If you don't want that then just don't do the RCA Academy, just stick with ARC training and you'll only be expected to do packages. Finally, the "evaluation" for how long routes should take you to deliver are in my opinion contingent on you being at 110% efficiency every day. You have to work extremely fast and not slow down to the slightest at any point during the day to meet those expectations. Mere seconds wasted on some movements/tasks can mean hours added to your day.