emm... the question is, is practicing on chromatic, scale could improve my speed and dexterity?
if you start slowly, make sure every note is clear, and slowly build up, yes. But whenever you miss a note start over, otherwise you will be sloppy and that's the last thing you want
"Don't play what's there; play what's NOT there" - Miles Davis
Yeah, the chromatic scale is quite useful, as a warm up. A slight variation which is much more common is refered to as the "1234" exersise where you basically play four consecutive frets on each sting. The problem with this is that you can do this easily as there is no differentiation between strings, its all the same pattern.

Scales on the other hand are much better to improve dexterity. With them, you need to be able to use different fingers at high speeds. This will make you much better and more used to playing different patterns on each string, rather than being limitited to using one after the other in equal steps, which you do in the 1234.

Overall I would advise not to wholly concentrate on the chormatic scale as a speed trainer. It will get your speed up eventually, but by that time your fingers would be so constricted that it would be horribly awkward when playing scales at high speeds. Warm up with it, have some string skippin with it, but then crash into some proper scales.
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what notorious said, i always start playing chromatics for 10-15 minutes, then work into minor scales or something
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