Thanks for the replies. So it seems it's a guitar only effects.
..Anyway, I've just upgraded to Guitar Rig 5 recently, and I have not even use it much. I've been using very little effects on guitar/bass lately, more towards Pro Channel compressors / eq on electric bass. For guitar, I'm recording more nylon string acoustic/silent guitar, not much requirement for effects either (compressor/eq/reverb most of the time).
But at 99/= it's quite tempting and I think the offer will be at the store for a while.