I am very satisfied with this combination. Everything has to work right away (video tutorial about the settings on Youtube can be helpful).
Flash sync speed in the SLT-A57 max. 1/200 sec.
The ability to control everything from the controller to the camera is really convenient (performance and Zoom).
I would buy all three again.
PS: Do not forget, there is a manual flash. But I think if you practice a bit, it works already.