The F12 button is not always the hotkey for dashboard. On laptops it's F11 for example, because the F12 key ejects cds.
The shortcut may be turned off to.
To check that go to Sytem Preferences, Keyboard and Shortcuts. Check what shortcut the Dashboard has or if it's unactive.
There is no reason for this not to work.
I also know that this is very old but there are ppl who don't want to mess With the Terminal. Thats why i made this app, that also saves time, because you dont have to type anything.