Ah that sorted it, using Genymotion was on API17. Moved up to API22 and all is well.
Next questions:
Is it possible to have multi-select with this extension?
Is it possible to "save the state" so that one can re-open a session and still have radio buttons checked? (e.g. if two buttons are checked, session saved, then on return, two buttons are still checked)
Is it possible to remove the check if you click on a button again?
Thanks
Tim