I use 'em sometimes..have one for the Metz 60CT and my nikon SB's..

I think you only point flash head directly at subject if you have a ttl camera..otherwise, best to angle them up about 45 degrees to strait up.

There's at least one stop loss...I usually bump the output on the nikon flash unit one stop, and add half stop to exposure settiing.
On the metz, if you have a ttl connection, I would adjust one stop to start.

They do soften edges of shadows somewhat nicely.