I have been on aza since 2003 with a two year pause from 2008 to 2010. It's an effective drug for many, altough after so may years on it I can say it alone can't keep you in remission, diet, sport, stress relief, vitamin therapy etc. has to go along with it.
Also, the dosage is key. For the first two years I was on just 100mg and at my body weight back then 70kg) that was just not enough. I am at 150mg today and that's at the lower boundary for me (I currently weigh 77kg).
Never experienced any side effects. The 8 weekly blood tests are the only thing that is required as checks.