The S701 hub is notably smaller and lighter than the S501, but it produces only half the output: 1.5W instead of 3W. (All other dynamo hubs we carry produce 3W).
This hub is intended for city use, it's not intended to power the super-bright Luxos lights or to charge smart devices. It will do both, but not as well. A great front light to run with this hub is the B&M Eyc or Eyc T(and any B&M tail light).
Note that for $150, the Shutter Precision hubs are actually lighter and produce 3W.
For use with centerlock rotors.