We took one of the bike tours from the sister ship Island Star last October. I think they are run by the same company. It was really enjoyable and one of the best days of the holiday. There were two groups and you could chose whether to take the slightly longer(and more strenuous!) route, or an easier one.We took the latter and had a good time. The guide was really nice and didn't go too fast! We had a couple of stops en route,including one at a cafe for a much needed drink. Hope this helps - enjoy your cruise.
We were also on Island Star this July and although we didn't do a bike ride we met a number of people who did. As Clayton has already said, they divide the group into experienced and 'the nervous'. We people we spoke to had been a bit unsure about doing the ride but thoroughly recommended it as they were well looked after. One lady hadn't ridden a bike for over 30 years but once she got going had a really enjoyable day. There is a bike hire desk on the ship where you can discuss any issues in advance. Go for it!
In August we did the bike tour in Menorca where we biked from Mahon to the south of the Island. It was fabulous and was very relaxed and the bikes are great. It wasnt strenuous and the guides look after you. It was one of the highlights of the whole trip and my 13 year old son loved it. We biked down country lanes with whitewashed houses and farms and reached a beautiful white sandy beach for a swim and some lunch before heading back along the coast road and back to the ship . 5 hours in all , very easy, amd all for £29 each - cant beat it.