If you equip “Nitro Unit” to a monster on your opponent’s side of the field, then you take control of that monster, “Nitro Unit” is destroyed because the monster is no longer on your opponent’s side of the field.
If your opponent controls your monster, and you target it with “Nitro Unit”, but your opponent chains “Remove Brainwashing”, “Nitro Unit” is destroyed because its target is no longer on your opponent’s side of the field when “Nitro Unit” resolves.
When the monster equipped with “Nitro Unit” is destroyed and sent to the Graveyard as a result of battle, the effect of “Nitro Unit” can be chained to.
The damage inflicted by “Nitro Unit” is based on the equipped monster’s original ATK (in the Graveyard).