The word isomorphism comes from ancient Greek, 'Iso' means 'equal' and 'morph' means 'form' or 'shape'. It means that intervals and thus chords always have the same shape regardless of the key or the root note. For example, a major chord always has the same shape, no matter if it's a C major, Gb major or A# major chord. All you have to do is learn the shape of a major chord once and then move that shape to the desired root note.

The classical piano is not isomorphic. A major chord can have different shapes, sometimes black keys are involved and fingers need to be stretched and elevated, sometimes not. At the same time, the same shape can lead to different chord types. Take the shape of a C major chord for example: Three white keys, using every other white key. Move that exact shape to the right and you get a D minor chord. So, same shape, but different chord type (from major to minor).

The same holds for scales. On the classical piano the fingering of a major scale depends on the key and thus all twelve major scales have to be practiced individually. On the Janko, one only needs to practice the major keys once and can apply the exact same fingering in all keys.

The answer is three-fold:

1. In many pieces and in particularly in Jazz, the key is changed pretty frequently. One probably wouldn't want to use the transpose button all the time during one tune. Using the transpose button only really makes sense if a whole tune/song stays in one key. One then transposes the tuning to the key one is most comfortable with. With the Janko, this problem doesn't exist. All keys are equal to play, so to transpose a song or change the key during a song, one can apply the exact same chord shapes but just move everything to the left or right.

2. Acoustic pianos don't have a transpose button, so if one wants to master the acoustic piano and be able to adopt to others (singers might want to change the key because of the properties of their voice, other instruments might feel more comfortable in keys that are uncomfortable on the classical piano) one needs to be able to play in all keys.

3. Even if one exclusively plays on keyboards with a transpose button, one might still be the urge to master the whole instrument and not for example ignore all the black keys and only play the white keys plus using the transpose button.

I definitely think so. The muscle memory simply works best if there are a few shapes that are constantly repeated. Instead of having different chord shapes and scale fingerings for all the twelve keys, with the Janko, chord shapes and scale fingering are the same for all keys.

The learning curve might be a bit steeper in the beginning because the hands have to get used to the feeling of the multiple rows of the Janko. But once used to it, the repetition effect kicks in. There are only a few shapes to learn and then one can easily apply them in all keys.

And the learning process is also really rewarding. When practicing, for example, a certain chord progression, one always knows that one is practicing all keys at once. One the classical piano, on the other hand, practicing a chord progression in one key might sometimes feel a bit frustrating knowing that one has eleven other keys ahead of one until one has really mastered it.

On the classical piano one feels where one is by means of the irregular pattern of black keys. On the Janko, the key layout is regular. Thus, one indeed doesn't feel where exactly one is. For playing a first note one needs to look at the keys. But once you have played one note, from then on you don't need to look at the keys anymore. Since intervals always have the same shape on the Janko, your fingers quickly learn how far to jump from one note another.

Playing the Janko means playing, thinking and feeling in relative terms instead of absolute. You don't think "I'm playing an A right now and next need to go up to C", you rather think "I'm going up a minor third", and your fingers know how a minor third feels like.

So yes, once your fingers have played the first note, you don't need to look at the keys anymore. You think in terms of levels and intervals and your fingers know what to do.