The MK-GT620 is a flash commander that triggers with a 2.4Ghz signal, designed for the MK-R200.
The MK-GT620 is very similar to the Nikon SU800 but at a fraction of the price. It uses 2xAA and communicates using 2.4GHz radio frequency signals so no line of sight is required.
Also sold as a set in MK-MT24.
This is the new version, not compatible with the old version.
SONY version is currently out of stock.