Our cruise ship had docked in Corfu for the day and we took a tour through the ship in conjugation with this group. The tour lasted about 5 hours, and the biking was all on the asphalt road. I went with my 57 year old dad and both of us are in good shape, so the overall feel for us was good since the uphill was a bit challenging.
For less experienced cyclists, the tour is still ideal since the uphill doesn’t last long and there is an optional extension to a small church at the top of a climb (views recommended). The scenery is very rewarding and the guides are excellent.