This one is not quite useful as it works like on/off trigger, but the one, which can be used as a direct replacement of Ctrl-X or Meta-X will be quite useful. (I am actually Vim user, so I had to ask my Emacs guys on what will be useful with the pedal)

Same, that's why I asked. I know Emacs has various 'modes', like haskell-mode, org-mode, SLIME, etc., but I don't how or if a footpedal would make sense for that. I don't think Emacs users switch between those modes as frequently as Vim users switch between our main modes.