Pros
As flexible as you could ever dream, tons of paid down time, great if you are active and like to move. Planes are cool. Free flights are sweet.
Cons
Compared to other major airlines, every system is outdated. Bidding, shift trading, OT sign ups, even the Transfer Run system is like in the 2000s. No limit on hours you can work, which is a pro until they mando you off of a 24 hour shift. Standby flying is lacking compared to other airlines, if only because of a lack of international routes, remember Southwest is domestic only while United is basically global.