Rented this movie for a bit of nostalgia, having watched it in the 80s, as a teen, on VHS. It really was a nostalgic experience as the DVD version appears to have been directly taken from a videotape, complete with washed-out colours, on-screen glitches and frame jumps, all of which actually made it more entertaining to watch!
The movie itself is, frankly, awful: a story that makes no sense, dreadful voice-over, incompetent and limp directing, and peculiar scenes such as the American line dancing group that randomly appears. What Lee Van Cleef is doing in it I have no idea either. As for the martial arts... The Octagon barely qualifies as a 'martial arts movie'. You really have to wonder how films like this ever got any funding to be made in the first place.
In short, I would advise using your rental credit up on something else.