error414 Long storry short, SmartAudio is built in the Graphical OSD. As there is no 20x20 FC with graphical OSD, no graphical OSD means no smart audio (equals no VTX change on 20x20 FC).
Regarding the menus, as far as the graphical OSD is concerned, you can flip OSD layouts with an accessory channel. So from a toggle switch you can have one layout with AHI, One layout with navigation stuff, etc... The menu itself is one of these OSD "layouts". Once the menu is enabled by the switch, you can navigate with the sticks.
The process is much more reassuring than the MWOSD that requires to raise the throttle up to the middle position in order to enable the menu (playing with throttle is not a good idea!). Also, the navigation is much more smooth in the graphical OSD than MWOSD: due to the fact that the stick inputs are converted into MSP messgaes and sent to another board, there is a bit of lag in the MWOSD setup, whereas things are much faster with the seppuku (or Brain RE1). The lag on MWOSD is not really an issue, but enabling the menu and navigating through the menus takes more time.