As williaty noted, they do just push on. For the two-click, you have to push past both stops but there's no button-pressing involved.
I do have some brass couplers that require less effort than the pushbutton style. But I still prefer the Prevost over them, especially over the long haul. I haven't cross-sectioned one, but they seem to hold up very well. In part that's proably due to all of the mechanicals being internal. I wish I could say that about my Milton pushbutton safety couplers. I'm hoping I just got some from a bad batch, but I've had two of them start jamming in less than 6 months. The only disappointing product I've ever received from Milton.