We did this last May, and it was great, even terrific. We had wanted to do it in the spring of 2015, but missed it. Unfortunately it was pouring the day we took the tour, and I do mean pouring.
So, we did do the Vatican museum and everyone on the tour agreed to shorten the garden tour and headed to the train. Yes, it is kind of an ' exclusive' feeling going out of the Vatican train station, what we considered a real treat. When we reached Castel Gandolfo some people got off the train and then the rest of us continued to Albano.
From there we were all supposed to take the open (little tour) train to see more gardens, but Rob and I opted to do the tour inside of The Popes summer residence (which had not been open when we stayed in Grottoferrata a few years ago). After which we found a warm and dry restaurant looking out over the lake.
A great day even if the weather did not cooperate. As a matter of fact we are seriously considering taking the tour again this coming May.
We highly recommend doing this full day tour, well worth the relatively inexpensive experience. Wendy and a Rob