Biggest con to the CCA position is the fluctuation in hours, schedule, and routes you deliver every day. The CCA position was basically created to diminish the amount of overtime that the regulars would have to work. In other words, CCA's were created as a means of saving the company money. Everything in the Post Office is based on seniority. So as a CCA, you don't get offered the regular position until one of them retires/quits/transfers/dies. Literally. So if you're looking to become a CCA with the hopes of making regular as quickly as possible, inquire with the Postmaster on how long it would be. If the office you're applying for has regulars who are all in their 30s and 40s with a bunch of other CCAs already, chances are you ain't making regular anytime soon. It could honestly be YEARS before you even get close. To make matters worse, because everything is based on seniority, whatever CCA has the most tenure at the time a regular position opens, they are offered that position even if they are clearly not the best option out of all the CCAs.
Also, expect to never have a set schedule. Even on your days off, your phone could ring at 6 in the morning from your boss saying they need you in. If you're not down with fluctuating hours and days off, you probably won't do well here.