A Mini Lesson: "Once Per Turn"

Hello! It's HolyLobsters with a mini lesson on commonly misunderstood topics. I'll Try to provide You guies' mini lessons once per week if time allows!

Now let's get to it!
"Once per turn" has a bunch of different clauses(rulings) that can be differentiated by small text.

Let's take Red-Eyes Darkness Metal Dragon as an example.
"Once per turn: You can Special Summon 1 Dragon-Type monster from your hand or Graveyard, except "Red-Eyes Darkness Metal Dragon"
This "Once per turn" can be reset by flipping facedown/leaving the field and returning. You can also use this effect multiple times if you control multiple copies, but each copy once before having to reset that copy.

Let's reword REDMD's effect to "Once per copy without leaving the field, You can Special Summon 1 Dragon-Type monster from your hand or Graveyard, except "Red-Eyes Darkness Metal Dragon"

Now, let's look at another "Once per turn" clause.
Harpie Channeler

Pay close attention to the text: "You can only use this effect of "Harpie Channeler" once per turn."
This is NOT THE SAME as REDMD. This text prevents the card from being reset, or multiple copies being able to use the effect. This is due to the "you can only use this effect" in the text. It forbids you from activating the effect if done so previously.

Now this part goes hand in hand with the "Once per turn" clause.
Ignition VS Quick effect:

Ignition effects are those that you activate manually, such as Blackwing - Gale the Whirlwind and are Spell Speed 1, which cannot chain to anything due to being too slow.
Furthermore, anything under chain link 2 cannot be activated on your opponents turn. This means effects with
"Once per turn" can only be used on your turn.
However quick effects are different. They are the only monster effect that can manually chain to other effects.
Wind-Up Rabbit is an example of this.
What seperates Quick Effects Vs Trigger Effects is again small text in the wording.
Monsters with this text:"During either player's turn:" or "You can use this effect during either players turn" are quick effects, the key word is "either players"