I was not certain that I needed flash as a) the new Pens are great in reasonable available light and b) I had an FL-20 flash already.
All other Olympus flashes and compatibles I tried work but are very top heavy. Having eventually tried an FL-14 I found that it was better balanced and seemed to give more consistent results than even the FL-20.
In summary the Olympus EP-1 and the FL-14 is a fun system that is very different to my slrs but will produce first class results in the right hands.