You gain the following benefits.
Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20.

Superior Dual Wielding. When you take the Attack action, you can treat a Melee weapon that lacks the Light and Two-Handed properties as if it has the Light property.

Crossing Swings. When you make an extra attack as a result of using a weapon that has the Light property, you can treat one of the previous attack rolls made on that turn as the extra attack's result at a 1d6 penalty.

Twinned Touch Training. If you also have the Two-Weapon Fighting feat, Dual Wielder is treated as Dual Weapon Master regardless if you picked this feat.