@The-Acre
Please before buy a GS300 do a Testdrive with a GS450h, after this you never buy a GS300
I am from Germany and buy in 10/2017 in GB a 2007 GS450h, in your Country a enough good cheap 450h for selling.
Here is a product from a other company i think i does the same but it is much cheaper for both products you need connection kit for the handy.
https://car-solutions.com/en/gvif-interface-for-lexus-toyota-land-rover-nissan-jaguar.php