I use this exercise as the basis for lots of good technique reinforcement and legato playing.
I approach exercises as a way to prepare the fingers for any eventuality when playing, you are not having to isolate a ‘difficult’ section of music and repeat thousands of times to be able to play with ease - it is better to be prepared for these challenges ahead of time.
I call it the chromatic, but it is really just the four fingers being placed one at a time on adjacent frets in order, once the fourth finger has played you move onto the next string. I find that playing in the higher positions takes away the need to stretch unnecessarily - actually, one of the important things to watch out for is perfect LH finger placement, right up to the fret wire (it’s amazing how little effort is needed to create a clear, buzz-free note).
The right hand can play using i and m alternating, actually it's better (if each note is played once) that m is used first and then i, to avoid an awkward string crossing. Once the left hand is solid, then the chromatic can be used to practise different RH combinations, m and a (a and m), i and a (a and i), p and one I love (but most students are initially horrified at) is i, m and a which combines a sequence of three plucks on the RH with four notes for the LH making a straightforward pattern difficult to adjust to without a lot of concentration.
I would say, to start, that each note should be sounded twice or three or four times and therefore slowing down the LH finger movements, but keeping the rhythm regular - this also gives the RH fingers a greater workout.
It is even a good idea to repeat the exercise silently, without sounding the note at all with the RH fingers. This is a great way to focus our efforts completely on the left hand - as soon as we have to concentrate on something else it becomes too much of a challenge and detrimental to speedy development.
However, besides these different approaches to the exercise, I created the sticky chromatic (explained in the vid) to focus the fingers on (eventually) hovering over the frets when not in use. There is also a synchronisation issue if the fingers are stretched out uncontrollably, they have a long way to travel to the fret and tension and stress develop. Once the sticky chromatic is natural to play, the stickiness can be dropped and fingers can release from the frets when not needed for a note to sound, gently curled (and therefore relaxed) and prepared to fret when needed.
As with all playing it is best to play slowly with a steady beat whilst counting aloud.