Musical instruments can be categoried in two big families:
Chord instruments such as guitar and piano that allow you to compose,
arrange and accompany. 
And ‘one-note’ instruments such as
the saxophone, the violin and the voice where you have constant control over the volume, the pitch and timbre during the duration of the note and
where you can slide from note to note.
Where would you place the Kelstone?
Most people will place the Kelstone in the first family: chord instruments.

The Kelstone is part of the ‘one-note’ instrument family! 

Because the new position of the hand and the length of the strings, the player has control over the length, the volume and vibrato of a note.

This new fine motoric skill is essential and extremely
innovative on the Kelstone!

Rather than the fact that you have 9 strings at your disposal, a range of more than 5 octaves or the possibilty ot play 2 separate musical parts .

The hand lies on top of the string, in front of the player, clearly visible and in harmony with gravity.
Extreme and extremely subtle slidings and bendings give control over the envelope of the note.
Rubbing the string over the frets prolongs the duration of the note like a bow on a violin does.

In that sense, the Kelstone has 1 string, 9 times!
You look at a string literally from a different angle!

Only secondarily, after a lot of practice the Kelstone becomes also a member of the chord family.

All this makes a big difference. 
I like to compare the Kelstone with snowboard.
Guitar and piano would be ski’s some 30 years ago (and I’m still fan of both). 
If you start on the snowboard thinking you still need poles,
it will be hard to explore it’s potential.

Playing chords on the Kelstone is not that hard but does take some practise as the area to hit a note nicely and clearly is somewhat smaller than on a keyboard.
But still an awful lot bigger than in the case of two-hand tapping on the guitar.

If the guitar is basically a pluck and strum instrument, the Chapman Stick a tap instrument, then the Kelstone is a slide / bend / hammer-on / pull-off / muting instrument.

As on other stringed instrument but unlike on the piano, the strings have to be muted. This is very important to have a nice sound and also to constantly feel the strings. On the Kelstone, muting becomes a musical action, an expression like a slide of a vibrato.

Approaching the Kelstone as a ‘one note’ instrument allows you to play from the first minute.
It’s like Brother Jacob on the piano that anybody can play
in two minutes.
One string, with one finger of each hand, as it is also a part of the precussive instrument family:

‘The Kelstone builds on the tradition of percussion
and key instruments 
in harmony with gravitystable on a stand (separate from the player who can move freely),  
clearly visible and an expressive action away from the player
towards the audience.’ 

Since the guitar turned electric and you have access to features such as

  • feedback (lenght of the note)
  • the whammy bar (vibrato and pitch) 
  • the volume knob

it has also become a major ‘One-Note‘ instrument.
Synthesis changed of course everything for the piano.
And string and wind instruments are part of the chord family if you arrange several of them in an orchestra.

Very interesting what Roger Linn wrote in his article
 ‘What’s wrong with acoustic instruments’ 
and how he concludes with ‘So what is needed in a new musical instrument?’: 

‘In my view, if the goal for a new instrument is to perform highly expressive music based on 12-tones per octavethen I think the following are good design requirements 

  •  The human interface should be optimized for ease of playingnot limited by the need for acoustic sound generation. For this reasonthe sound should be generated by synthesis 
  • It should be polyphonic 
  • It should be highly expressiveable to control each note’s loudness, pitch and timbre continously over time. It should be able to perform convincing performances of expressive traditional acoustic instruments 
  • The note layout should be isomorphic— for any given chord or scalethe fingering is the same for all 12 musical keys 
  • Efficiently use of hand/finger gestures. Like a piano keyboard, only one finger should be required to produce a single note 
  • Easy to play in tune, yet subtle pitch nuances are possibleYou should be able to easily play notes in tune while also playing vibrato, bend and other pitch nuances.’(©Roger Linn)

The  Kelstone has all the requirements that Mr Lynn stated apart from generating the sound by synthesis.
MIDI is an option for the future, something like the guitar synthesizer (which is not essential).

I don’t think that there is anything wrong with acoustic instruments, on the contrary.
Acoustic instruments have more harmonics and humans are designed for very complex sounds in nature, more than 44,100 Hz!

Harmonics and hammering/tapping

The harmonics of a note are very poor using the hammering technique on a string.
With strumming and plucking, different 
places on the string  create different harmonics.
With hammeringyou hammer on the total length of the vibrating part of the string.
So your fundamental frequency will be strong but little extra harmonics are created. 
This is why it is advisable to vibrate (bend up and down over the fret) each note (and even in chords). 
Most of the time this vibration after the note has being played is
also done when playing ‘one-note-expressive
instruments like the saxophone and violin.

Basically there are three things that are important when you start on the Kelstone: 

  • The Kelstone is in the first place a one-note instrument like the saxophone, violin and voice. Chords come later after a lot of practise. 
  • Muting of the strings is primordial.
  • The ‘tasting‘ of the strings with the fingers before playing is primordial.
  • Vibrating the strings is primordial.
  • Any technique can be used and what is very interesting on the Kelstone
    is that the finger that makes
    the action to generate a note
    is not necessarily on top of that note.
    This is strange in the beginning
    but does stimulate the brain to get a new view on how to make music. 

Estimated studytime compared to guitar and piano:

Level 1 for chords: accompany a singer: simple popsong-no reading & with help of a Youtube tutorial 
Level 1 for melody: simple tune, riff, bassline, doubling the leadvocals-no reading & with help of a Youtube tutorial  

  Piano-Synth  Guitar  Kelstone 
Chords-Level 1  2 months  1 month  6 months 
Melody-Level 1  1 day  1 month  1 day