I have list of buttons that can be pressed or unpressed individually (like checkbox functionality). Some of the buttons can also have some attributes (+ or -), but it's uncommon to select those attributes, the far most common is just to use the initial button values.
See my attached image:
The idea of the design is to let users just click the values they want, which is a pretty fast way of doing the choices. If the user want's to add the attribut + or - (available on "b" and "c") - press the button and after some delay a drop down list appears with the choices.
The disadvantage of this, as I see it, is that I try to merge two standard UI elements - a button and a drop down list, is it intuitive?
Unfortunately I don't have the time to make a user testing scenario to test this.
Can I get some feedback on this? Can you suggest a better way of adding + or - to "b" and "c"?