If you plan to use activeadmin you have to be warned that  by using active admin you are supporting two back ends – yours and the one for active admin.
So if you have time to work for someone else go with active admin. else just do it your self.
Don’t use it!
There is one rumor that nothing starting with active* was good product. ActiveDirectory for ActiveX…. I was wondering are there exceptions ActiveSupport, ActiveRecord….