The TOSR04 module uses FT232RL USB to UART chip. Before using the TOSR04 you will need to download theFT232RL Driver. A full datasheet for the relays used on the TOSR04 is here: G5LA datasheet. Connect the TOSR04 and windows will detect it and ask for the drivers.
In general it is a good product.
There is one design issue (from my point of view). Relay's state are reset on each UART open port or USB connect (when powered from power jack). For some cases it is not an issue but on some cases you want to keep relay state even when open PC terminal.
Controller reset signal is connected to FTDI DTR (Data Terminal Ready) signal that toggles each time UART driver starts when open terminal.
This connection can be remove by removing a capacitor located close to the reset pin.