Rikke:

I understand now. I think you are in fact referring to the "controller-synth" boards, which tend to be 2-3 times more expensive than a plain MIDI controller board. Perhaps more , in the case of top-rated Novation and others.

These keyboards have -- I believe -- all of the MIDI controller functions AND a built-in certain number of "synth voices". I assume these are in fact various popular synth sounds for playing a melody and/or solo, depending on the KB size, etc. I personally have not yet seen one in action.

Since you would have to be connected still to the computer w/soundcard, VSTi stuff, etc., OMB, to really play completely with thythm, I myself see no great advantage for extra expense, except for convenient playing around with "synth" melodies without any backing. I do not believe these KB have sampling for onboard storage, etc. Might be wrong there, check reviews of latest.

Myself, I am new to the world of soundfonts and all of the variety that this brings to the arranger scene as well. I doubt I will be investing in another full-fledged arranger KB again.