Is the RS audio tour sufficient or should we opt for the tour guide companies?
It is personal preference. While the RS audio guides are good, a live tour guide is always better, IMO. The big reason - you can ask questions and get answers.
i just did the RS audio tour last week and found it engaging but a bit light. i didn't learn too much. you can listen to a couple of minutes of it before you decide.
There is very good signage at the colosseum so that combined with an audio guide is usually enough information. I haven't listened to the RS audio guides. The official ones at the colosseum are very good.
Donna