My 430EX mk1 swivels both ways not one, with the camera at your eye normally it goes 90 degrees right or 180 degrees left. Which is fine, but when you're in portrait that turns into 90 degrees to vertical, or 180 degrees past the ground to straight behind you.
Which (as I think Bryan noted in a review) is the completely pointless direction, because the best direction would be overhead behind you where that won't reach. Or is that what you meant by 'one way'?
(unless you hold your camera in portrait the 'wrong' way with shutter on the bottom like i've seen a lot of people do with a P&S, even my mum holds her K5 like a gumby in portrait because her left eye is better (or something).
But doesn't the 580EX do that too? or does the 580 go 180 degrees both ways?
Sounds like these metz ones might not be too bad in theory if they go the whole way, do they work as an optical-slave from, say, a 7D?