In the simple tone generator there is a slider to change frequency.
It would be useful and fun if there was a slider for each tone in the multi generator.
Fun for the students or for the teacher?
Anyhow, the next version of phyphox will support conditional visibility of UI elements. This means that we can have a dropdown at the top of the tone generator to switch between "Single", "Dual" and "Advanced" that would then show or hide different controls. I have to check what two sliders look like, but that might indeed be a good idea here.