I went on one a few years ago and know two people going on them this week
Mine was predominately women who had been nicked on the school run, i think i did mine a few days after coming back from Germany so had admitted driving at 165mph on a motorway
Bits I found useful were the rural A and B roads and added spotting of danger, this area has had biggest impact and also reiterating the space between vehciles in order to have time to react, all be it the gap is often taken up by others who see this as an opportunity
The 30mph was laid on a bit thick for the school run brigade who were the most hypocritical of the lot