How does the Savage Attacker feat interact with fighter's martial architype Vigilant Defender?

Question

Savage Attacker

Once per turn when you roll damage for a melee weapon attack, you can reroll the weapon's damage dice and use either total.

Vigilant Defender

Starting at 18th level, you respond to danger with extraordinary vigilance. In combat, you get a special reaction that you can take once on every creature's turn, except your turn. You can use this special reaction only to make an opportunity attack, and you can't use it on the same turn that you take your normal reaction.

Since Vigilant Defender says you get to take the special reaction "on every creature's turn" and Savage Attacker says "once per turn" does that mean you can activate Savage Attacker on every special opportunity attack? I would have assumed not, but then this post from RPGbot was super confusing:

Savage Attacker is a bad feat. But hear me out: Once you get Vigilant Defender, you’re going to make a lot of attacks on a lot of turns. Savage Attacker works once per turn, so you can use it on every Opportunity Attack in addition to using it once on your own turn. Combined with the reroll from Piercer, you’re going to consistently roll well on that d12 damage die.

So it say's Savage Attacker is a bad feat, but then it says you get to activate it on every opportunity attack... which sounds great. So which is it?!

Answer 1

Once per turn means once per turn

Each use of Vigilant Defender necessarily happens on a different turn and each can benefit from Savage Attacker.

Answer 2

You're confusing turns and rounds.

Rounds of combat are one measurement of time. Once everyone has completed a turn, including monsters, that's the end of the Round. It may have some etymological basis in 'going around the table'.

Turns are each individual character or enemy's turn. There are as many turns per round as there are participants in the combat.

If an ability says it may be used once per turn, then if you are able to trigger that ability on another creature's turn, you may use it even if you have used it already this round on your own turn.

This is why a rogue can sneak attack on their Opportunity Attack even if they have already sneak attacked on their turn.