No, there is no Better beamer that fits the built in flash on the Sony RX10 IV camera.

The FX1 would be a better fit but you will still have to modify your flash to make a snug fit by using weather stripping.

Yes, it will work.

Heather S, why do you say it is only compatible with the SB900 and SB910 when the specs above say it is compatible with the SB5000?

They changed sizes on me. This one does not even fit my Canon Flash

Yes, the FX6 Better Beamer can also fit the Canon Speedlite 600EX II RT.

The key dimension is going to be that of the height of the sides of the flash heads, from the bottom of the head to the top of it when it's facing forward. The Sunpak 555 is going to be especially challenging to fit because the head itself is difficult to access, so that would be less likely to work. But as for your Metz 45, if the sides are 1.5" or only very slightly shorter (please be sure to measure them) and flat (not curved like the Nikon SB-80DX), the FX4's so-called "ears" which grab onto 1.5" high sides would make it the best fit of the Better Beamer series (BH #VIFX4): https://bhpho.to/3oLAsHW It should be noted that your experience and preferences with respect to fit may vary, so we would invite you to make your purchase and hold onto your packaging materials for a return if needed, in accordance with with our return policy: https://bhpho.to/3yuPExH

The Visual Echoes FX6 is designed to specifically fit the Nikon SB-900 and SB-910 flashes and will not fit the Bolt VX710N. Try the Visual Echoes FX4 for a better fit: http://bhpho.to/TWM4YA