Thinking about buying this board.
Does it work with VHDL or do you simply write sketches in the IDE provided by arduino?
There's two component - fpga, which is programmed in HDL of your preference, and arduino mcu running sketches written in arduino IDE.
There are two fpga "libraries" - VidorGraphics and VidorPeripherals, providing some predefined functionality. So you need to write only arduino sketches to make use of those.
But you can also make your own fpga library, so you will write both - arduino scketch and fpga configuration stream.