Oracle 11gR2 Automatic SQL Tuning

Oracle Linux
Oracle 11g.
Stand alone Instance/DB

Looking at enabling Oracle 11g Automatic SQL Tuning.
To a large extent startup parameters have been tuned.

Just want to leverage this feature in 11g.

How stable/reliable is this?
Any concerns that I need to be watching out for.

Will do a lot of testing in the lower environments.

Any information/help is appreciated.
Thank you