The pro's are that since you are using two anabolic steroids at the same time, you will gain slow, solid muscle growth that you'll have a better chance of keeping. Not to mention the strength gains you'll have while on! There are a few guys here that swear to highly anabolic cycles. Gearedup has posted many times that those are his favorite cycles.
The con's are that by using only anabolic compounds without an androgen, like test, you won't experience the fast size gains that many come to expect when doing a cycle. In addition, there is an excellent chance you'll have a diminished libido and a bad case of deca-dick. There is also a chance that you'll see some progesterone gyno symptoms, but those should be controllable by taking arimidex all the way through.