I would not like to do this often. Weeks of running on the roads and my bad knee has been fine. 26 minutes on the treadmill and it's hurting and a bit swollen. Also had to go slower than usual or I found myself drifting over the edge of the belt (in all fairness it's very compact). So just for times i really can't get outside...like now when we still have ice on the pavements after a week. I really didn't enjoy it much. The only thing that was easier was not having steep hills and slopes to contend with, and my maximum heart rate was much lower than normal, reflecting the lack of elevation.
But it is done and dusted, and Michael Johnson says I'm a runner. Woohoo!!!