Those bicycle dynamos were made by Miller, the Rolls Royce of dynamos but even so they were rather ineffective. In spite of having three per drogue the chance of even one working was pretty low. They had vanes with airflow directed onto them as a turning force but with unreliable results.
The airborne deterrent was trialled for two weeks in July 62 as Trial 448 and in spite of picking mid-summer the weather caused quite a few problems but I think the main reason it was dropped was the expense. As well as the fuel used there was a considerable amount dumped in order to get the Valiant tanker back on the ground to be ready for the next refuel with limited tanker availability.
The Mk16 HDU on the Valiant also differed from subsequent marks in that it was manually operated. The torque for trailing, refuel and wind was set by the Nav Rad using power or scoop settings via a Wheatstone bridge. This was not always reliable and many a hose trailed to five miles, stripping the brake to pieces. It was also possible for the hose to be unbalanced in refuel giving either a hard contact or the opposite with the hose running in as the receiver neared the drogue. These were early days and much to be learned.