Just saw this documentary and it's definitely worth a watch. There is none of the ignorant mainstream perceptions of the genre that you often see( such as Leone being the only good Italian Western director etc). And the critics that are interviewed are Italian western geeks such as Christopher Frayling, Alex Cox and Howard Hughes. All the great movies are mentioned, The Big Gundown, A Bullet for the General, Django, Django Kill, The Great Silence etc and a few of the key actors are talked about, Eastwood, Milian, Nero, Hill etc.
Plus there are interviews with most of the key participants (those that are still alive anyway), Franco Nero, Tomas Milian, Sergio Sollima, Ennio Morricone, Enzo Castarelli, Sergio Martino etc.
Not sure whether it would be worth buying as I've seen it's pretty expensive. Especially for something that is only 55 or so minutes long but absolutely worth a rental.