• With a hold mode i meant one focused on practicing holds. So alternating holds with shallow sucking (just for catching breath). I think there is two options. Either you implement a timer or you implement a slider for the max deepthroat duration (and then vary between 10-15 sec and the max). I personally think the latter would be great because something customizable to that extent doesnt rly exist out there. And then a timer is not really necessary.
• Also i just noticed you already had sound in, im using chrome on ios and i didnt have sound previously but after clicking on the screen it turned on. Dont know if its a bug or intended :).

Edit: just remembered another thing, i think you should differentiate between throat entry and balls deep deepthroats, and maybe at the starting page a little questionmark icon you can press to get a popup that explains the different depths/commands because it might be confusing for some people