We have never been big Hop on Hop off fans for a variety of reasons but you are right that many travelers do love the things. But in the case of the OP the HoHos are not much help. For example, the various Naples HoHo buses (at $28 per ticket) are only good for local travel. They are of no use for folks wanting to go to Herculanium, Pompeii, Capri, Ischia, etc. Since the overwhelming majority of cruisers prefer to leave the Naples environs for other places the HoHo is not helpful. As to Rome, we find it much easier (and a lot cheaper) to use our feet and perhaps add in a couple of trips on the fast Metro. Since one can purchase a BIRG ticket for 12 Euros in Civitavecchia, and that single ticket covers round trip train transportation between the port and Rome plus all days unlimited use of Rome's buses (not including the HoHo) and Metro. Using the HoHo would add nearly $60 to the cost for a couples day and you can spend a lot of valuable time waiting for the next bus, sitting in traffic, etc.