Now that was a fun watch. The Prog Rock Britannia documentary has the same setup and style. British documentaries generally have better writing and I thought this one was quite good.
For the early years you can tell they were lacking a wealth of musical and video material, so the selections are kind of sparse, but the quality of the interviews make up for it. Interesting that Burke from Budgie doesn't see them as being in the same category as Deep Purple or Black Sabbath.
I've always leaned toward British music, so seeing just this side of the metal equation was cool. I've never seen those Diamond Head music videos either, so bonus points!