It can hurt a little bit, and some people are more sensitive than others, just as different areas of the body are more sensitive than others.  The sensation is often described as a slight pinch or heat when the electricity is applied.  Topical numbing creams can be used for sensitive areas.

The treatment timeline will depend on the area and the density of the hair you're looking to remove, as well as the type of hair.   Hair grows in cycles and not all follicles are active at once.  It will take multiple sessions to treat.  Hormonal facial hair can be more stubborn to remove.  To treat a full beard, it will take consistent treatments for an average of two years.

Yes, electrolysis works on all hair, regardless of hair or skin color.

Yes, electrolysis works on all hair, regardless of hair or skin color.

Other hair removal methods are not permanent.  Electrolysis treats each hair follicle individually and destroys the cells and tiny blood vessels that contribute to hair regrowth.

Laser can be useful for hair reduction, it is not a permanent hair-removal method, and requires a particular hair color and skin complexion combination to work.  It is neither suitable for light or white hair, nor dark hair on dark skin. 

Waxing, threading, and plucking all remove the hair but the follicle remains active and the hair will regrow.

Shaving and trimming only treat the hair above the surface of the skin and do not reduce hair regrowth.