Great program, the sort of thing that the BBC can be proud of.
I bought the first, A series for about £5 which seemed fair enough.
I am not going to pay £20, in fact I would be unlikely to pay more than £5.
The BBC is already making its money from re-runs on Dave, but they do have to face the fact that they have therefore devalued their own product. If I want to see QI, it is on almost any day of the week and I have a PVR.