TomLC HZPiano. Wow, is this the most difficult instrument there is to learn to play? Two keyboards AND foot pedals. It looks impossible to me.
I can share some insight, since as I said earlier basically this was my first instrument.
The vast majority of these organs are not touch (velocity) sensitive, even though there are a few that there are. The vast majority do not have aftertouch either, even though that's a bit more common than the touch sensitivity. AFAIK none has polyphonic aftertouch.
Unless you want to learn to play Bach's fugues (which very few people do, see for one example, and check other things from the same guy!!) it's not very difficult to play the organ.
Most commonly, the left hand does blocked rootless chords (not even arpeggios, at most simple ones) and the foot does just the root of the chord, which on the piano one would play with the left hand doing great jumps in the left hand.
So my experience is that for the same level of playing (of course one could become the best virtuoso of an instrument and do incredible things), the organ is easier, as follows:
- the lack of touch sensitivity allows you to play sloppy and have one less thing to worry about
- the style of blocked chords in the left hand allow you to quickly learn the left hand and "forget about it" unlike in piano for which the LH is always hard
- the use of the foot is not that hard (actually it's easier) because
- - it's on the beat, rather than like the "syncopated" use of the piano pedal which need to happen off-the-beat to keep the sustain or the soft/unacorda happening before/after the notes have been played
- - in most cases it's just the root of the chord, or at most is alternating root and fifth
- - some players don't even use the pedal but instead rely on a separate person playing the bass
- - if you do play the pedals, you do have have a complication, but most inexpensive organs have only one octave and the pedals are big enough to find your way to it without too much effort (unlike the several-octave keyboard of the piano)
- - the fact that you play the pedal greatly simplify your use of the left hand, and especially removes all the big bass-chord jumps which are one of the most technically challenging aspects of playing modern piano solo
- the fact that there are two keyboards (called manuals, in Italian mano means hand) is actually a simplification too, since you don't have to worry about crashing one hand into the other or having to go above or below the other
- the keyboards are not weighted, so you can press and release keys faster more easily than on the piano (where the easy way to do faster would also cause louder, which you often don't want)
- you don't have to worry about hand injuries
- given all of this, your brain has plenty of "spare" energy to concentrate on melody alone -- hence often the virtuosi can play much faster on an organ that a similar piano virtuoso can on a piano