Nowadays I'm working with Primefaces and I have to choose between two date input controls from here: Popup vs button.
When clicking on the "Popup" text input, you are able to type the date and ALSO the calendar shows so you can select the date from it.
When clicking in the "button" text input you can only type and if you want to select from the calendar, you have to click the button to open it and select.
I think the one with the button is more clear about the expected results and specificity of the action, but the one without it gives the same functionality (I think the level of confusion that could bring is minimum because there's just 1 input and 1 final action) so I'm not sure about the button being really necessary.
Is there any reason why I should consider one over the other?
Have anyone tried it with users and noticed any difference?
Is there any study on the subject?