You gain the following benefits.

Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20.

Property Addition. You may add one property to a weapon as long as you have proficiency with it and it is one of your weapon mastery choices.

Property Remove. You may remove one property to a weapon as long as you have proficiency with it and it is one of your weapon mastery choices.