It is a very healthy, green, and quick way to visit all the top places and buildings in Rome. In around 4 hours you would have got good pictures of all main views of Rome, a general historical knowledge of each place, even some anecdoctes. In addition, you will enjoy biking, and skipping trafic jams because you will use pedestrian and narrow streets arriving in 5' from a view to next building, not polluting and not wasting time. Raccomended if you wish a general view before deciding which interiour buildings to visit. The hills are not hard climbing at all. Even a child could do it. You do not need to be a professional or very trained. Some little breaks if you need them.
I was really lucky, very sunny and not cold day and a November day (not other joined tourists doing the same tour): same price for a private bicycle tour.