Let me start with - if you don't know how to work with your 580EX II (or any other pro flash) MANUALLYdo anything you can to avoid using a flash at all.Using any strobe, automatically , TTL , can never get you the right resultsso the vivitar is just perfect to light your scene.The only con I might have is that the lowest power you can use is 1/32unlike my 580EX II 1/128but if you use reflectors/defusers and the right distanceit shouldn't be a problem.