The participants are hardly Guantanamo Bay residents.
I think it's a good idea, take some low-risk prisoners and teach them the ways of cycling: discipline, hard work, delayed gratification and to give prisoners something to aim for during the winter months as they work in the prison gym.
I saw a group of riders out training for it the other day, they are the sort of prisoners who are allowed small release periods, not high security detainees. They all get special clothes for the ride. It's also a way for the prison services to show the public that not all prisoners are low-life ready to kill ordinary citizens, the people on this ride will just be those who made stupid mistakes.
It's not like the old "chain gang" where workers would be forced into slave labour to clear roads, it's something more positive. I don't know if it will work but it's cheap, especially since many will spend the night... in prison as they tour from jail to jail!