I would strongly recommend Panasonic PE-20 or PE-28. I have a PE-20 of pocket size. Both of them have SLAVE SENSOR built in the back of the flash. so I carry my PE-20 in my pocket for incidental fill-in. Even without bracket, I can hold my PE-20 in my left hand a little bit left before my Z700 and has the onverhead flash on Z700 trigger my PE-20. Quality of Panasonic flashes are very durable. I also recommend Yashica C240 (though without slave sensor) for auto-output of the power based on the aperture you set on the flash. It is also of durable quality. I find that a slave sensor socket is very convenient for added fill-in because most current cameras have overhead flashes built-in to trigger slave sensors. A pocketable slave sensor with X-terminal cord (switchable between sensor or X-terminal) of billiards chalk size is available from local photo shop or on the internet. As to bracket, those with hot contacts are more convenient, but more expensive also. DX 7590 has X-terminal on the camera, so you can plug the cord of flash into X-terminal on youe DX7590. Watch out for the width of the socket for the flash on your bracket. A loose socket will cause your flash to drop and damage.