Glad to share our experience - both successes and failures.
We didn't do well with radio at first because we didn't have the right 'sales funnel' in place. In other words, our website wasn't setup to send people where we wanted them to go (which we're doing another relaunch here in a little while because we've learned more).
I will say that radio has been most effective with the conservative base of patients - ages 45 and up. We're in an area where we only have conservative talk radio, nothing on the left side of the aisle (which is unfortunate, because DPC is definitely non-partisan).
Hope this all helps a little bit...