Pros of the bike
You must control the bike when you are outdoors, pedaling with one leg and pushing yourself to the left or right around a corner with the other. So you are working both legs which would not be the same when you are on a stationary bike. It will not turn over and you don’t have to worry about falling or getting hit by a driver.
For maximum effectiveness and efficiency always do the natural exercise over the machine assisted. You will get more out of your workout and you will enjoy it more also. Now, there are cases where you might use the machine assisted for injuries or beginning a weight training program. Most of the time it’s makes just plain sense to go the natural way.