No doubt, exercise in any form is a good thing. Riding a bike is good because it is relatively low impact on your joints and bones, and it isn't as boring as running on a treadmill. The biggest negative is trying not to get run over if you live in a place where there are no bike trails.
My biggest question would be, do I get the same benefits if I coast a lot...like 40% of the time? If so, I'm in for sure!
Safety first