I did a thread asking about authorized fetch before switching it on, and no one seemed certain if there would be problems.
So, I did a trial period, and no one reported any problems reaching the accounts (I was asking via FediTips which wasn't on authorized fetch). And my hosting company said there weren't any problems at their end. So I just left it on.
As far as I can tell it does work now? Would like to hear if there are issues though.