To be fair, realistically, asking Siri to increase or lower volume is a joke, so it's fair to say there are no inline controls as you normally imagine them to be.
Siri increase volume
Siri increase volume
Siri increase volume
Siri decrease volume
Siri decrease volume
Siri decrease volume
Seems more caveman than simple direct controls.
Personally I still will buy these and just assume they have no volume controls and use my iPhone or whatever to adjust volume. Like any other headphone that has no inline controls. It's a downside but not too huge.