I was wondering if you buy this upgrade do all droids in the unit get vibroswords or does only one droid get a vibrosword.

They all get it. That's how Grenade and Armament upgrades work. If it was a Personnel or Heavy Weapon upgrade it would say "Add a XXXXXXX mini," and only that mini would have the weapon.

Ah cool, I couldn't find it in the rules reference. Thanks

3 hours ago, Dcoles said:

Ah cool, I couldn't find it in the rules reference. Thanks

Page 83 "Upgrade Cards" has the following bullet point:

"Some upgrade cards feature the hard point (󲉸), grenade (󲉾), armament (󲊉), crew (󲊈), or ordnance (󲊏), upgrade icons; these are weapon upgrades. These upgrades do not add any minis to a unit; instead, every mini in that unit may use that weapon when attacking the enemy."