Both share the same functionality. Roon Bridge is a software package that may be installed, but not distributed, on a computer, e.g., Raspberry Pi (ARM), Linux, macOS, and Windows.
In contrast, Roon Ready devices contain Roon software in firmware, and this is distributed, under licence, with retail equipment.
AFAIK, Gustard do not offer any Roon Ready devices, and should not ship with Roon Bridge (as this would be a licence violation.) You may be required to install Roon Bridge manually.
Likewise, it may not be supported by Roon (it isn’t listed on their Partners page.)
Nonetheless, if hardware supports volume control, you would be able to adjust this from the app.